Contributed
Poster Index
(all posters are to be max. 36" wide by
42"high) 
Posters
displays
Tuesday August 13

Posters
displays
Wednesday August 14

 Koji
Azuma
Classical analog of "quantum nonlocality without
entanglement"
 James
Bateman
Improving the efficiency of Nphoton superresolution
using an optical centroid measurement
 Salil
Bedkihal
Flux dependent effects in degenerate and symmetric
quantum doubledot AharonovBohm interferometer
 Aharon
Brodutch
Restricted, distributed quantum gates
 Zhu
Cao
Efficient Synchronization Scheme for Quantum Communication
 Aurelia
Chenu
Sunlight can not be viewed as a series of random
ultrafast pulses
 Greg
Dmochowski
Increasing The Giant Kerr Effect By Narrowing The
EIT Window Beyond The Signal Bandwidth
 Amir
Feizpour
Weakvalue Amplification of Lowlightlevel Cross
Phase Modulation
 Kent
Fisher
Quantum computing on encrypted data
Roohollah (Farid) Ghobadi Creating and detecting micromacro
photonnumber entanglement
 Roohollah
(Farid) Ghobadi
Creating and detecting micromacro photonnumber
entanglement
 Gilad
Gour
Universal Uncertainty Relations
 Horacio
Grinberg
Nonclassical effects in highly nonlinear twolevel
spin models
 Timur
Grinev
Coherent control and incoherent excitation dynamics
of pyrazine
 Andres
Estrada Guerra
NonMarkovian effects in the dynamics of entanglement
in high temperature limit
 Matin
Hallaji
Quantum control of population transfer between
vibrational states in an optical lattice
 Wolfram
Helwig
Absolutely Maximal Entanglement and Quantum Secret
Sharing
 Nathaniel
Johnston
On the Minimum Size of Unextendible Product Bases
 Dongpeng
Kang
Bragg reflection waveguides: The platform for monolithic
quantum optics in semiconductors
 Eric
Kopp
New Control Frontiers in Noiseless Subspace
 Hoi
Kwan Lau
Rapid laserfree ion cooling by controlled collision

 Juan
David Botero
On the Dynamics of Spin1/2 particles: A Phasespace
Pathintegral Approach
 Rolf
Horn
On chip generation of polarization entanglement
in a monolithic semiconductor waveguide
 Hoi
Kwan Lau
Quantum secret sharing with continuous variable
cluster states
 Xiongfeng
Ma
Experimental realization of measurementdeviceindependent
quantum key distribution
 Dylan
Mahler
Adaptive quantum state tomography improves accuracy
quadratically
 Sebastian
Duque Mesa
Relativistic Dynamical Quantum Nonlocality
 Leonardo
A Pachon
Coherent Phase Control in Closed and Open Quantum
Systems
 Alexandru
Paler
Resource Optimization in Topological Quantum Computation:
Verification.
 Kyungdeock
Park (Daniel)
Heat Bath Algorithmic Cooling and Multiple Rounds
Quantum Error Correction Using Nuclear and Electron
Spins
 Nicolas
Quesada
Selfcalibrating tomography for nonunitary processes
 Christoph
Reinhardt
Design of a Strong Optomechanical Trap
 Katja
Ried
Quantum process tomography with initial correlations
 Lee
Rozema
Experimental Demonstration of Quantum Data Compression
 Lena
Simine
Numerical simulations of molecular conducting junction:
transport and stability
 Cathal
Smyth and Dr. Gregory D. Scholes
A Method of Developing Analytical Multipartite
Measures for mixed Wlike States
 Xin
Song
Enhanced probing of fermionic interaction using
weakvalue amplification
 Zhiyuan
Tang
Experimental demonstration of polarization encoding
measurementdeviceindependent quantum key distribution
 Johan
F. Triana
The Quantum Limit at Thermal Equilibrium
 Timur
Tscherbul
Quantum coherent dynamics of Rydberg atoms driven
by cold blackbody radiation
 Tian
Wang
Demonstrating macroscopic entanglement based on
Kerr nonlinearities requires extreme phase resolution
 X.
Xing
Multidimensional quantum information based on temporal
photon modulation
 Feihu
Xu
Measurement Device Independent Quantum Key Distribution
in a Practical Setting
 Zhen
Zhang
Decoystate quantum key distribution with biased
basis choice
 Eric
Zhu
Broadband Polarization Entanglement Generation
in a Poled Fiber

WITHDRAWN
 Clement
Ampadu
Decoherence Matrix of the GudderSorkin Type for
Quantum Walks on Z^2 and the KonnoSegawa Conjecture
 Agata
M Branczyk
Optimised shaping of optical nonlinearities in
poled crystals
 Sinan
Bugu
Fusing Several Polarization Based Entangled Photonic
W States
 Peter
Cameron
Quantum Impedances, Entanglement, State Reduction,
and the Black Hole Information Paradox

 RayKuang
Lee
Spinflip for a ParityTime symmetric Hamiltonian
on the Bloch sphere
 Andreia
Mendonça Saguia
Onenorm geometric quantum discord under decoherence
 Angelo
Lucia
Stability of local quantum dissipative systems
 Vaibhav
Madhok
Information gain in tomography  A quantum signature
of chaos
 Shengjun
Wu
State and process tomography via weak measurements

Koji Azuma NTT Basic Research
Laboratories
Classical analog of "quantum nonlocality without entanglement"
Coauthors: Masato Koashi, Shinya Nakamura, and Nobuyuki Imoto
Quantum separable operations are defined as those that
cannot produce entanglement from separable states from scratch,
and it is known that they strictly surpass local operations
and classical communication (LOCC) in a number of tasks,
which is sometimes referred to as "quantum nonlocality
without entanglement." Here we consider a task with
such a gap regarding the tradeoff between state discrimination
and preservation of entanglement. We show that this task
has a complete classical analog, in which distant parties
attempt to preserve secrecy of given bits as much as possible
while they also try to discriminate whether their bits are
the same or not. This purely classical scenario is shown
to have the same amount of the gap as seen in the quantum
case. This fact suggests that the public communication (corresponding
to LOCC in the quantum case) is less powerful than "classical"
separable operations that cannot produce secret key from
scratch. As a result, contrary to a common belief that may
be inferred from previous known examples in quantum information
theory, quantum properties, such as nonorthogonality, measurement
backaction, and entanglement, are not essential in the existence
of a nonzero gap between the separable operations and LOCC.
This presentation is based on the paper in arXiv:1303.1269.
James Bateman, University of
Toronto
Improving the efficiency of Nphoton superresolution using
an optical centroid measurement
Coauthors: Lee A. Rozema, Amir Feizpour, Dylan H. Mahler,
Aephraim M.
Steinberg
Precise measurements using light and the precise manipulation
of light are essential to many modern technologies. The
resolution of the smallest possible features is required
in diverse applications ranging from technical fields such
as lithography to basic sciences and biomedical imaging.
However, these measurements face fundamental limits. For
instance, the resolution of spatial features is limited
by the diffraction of light. There has been much work towards
surpassing these limits using novel quantum states. The
socalled N00N is known to exhibit superresolution, displaying
an Nphoton interference pattern which is N times narrower
than that of classical light.
However, observing such a spatial interference pattern is
very inefficient. The probability of all N photons arriving
at the same point in space decreases exponentially with
N. Here, we experimentally overcome this hurdle by utilizing
an optical centroid measurement. By using an array of 11
single photon detectors, and measuring Nphoton correlations
among all 11 detectors we observe the spatial Nfold superresolution
without the exponential loss. We will present experimental
results for N=2 and progress towards N=3.
Salil Bedkihal University of
Toronto, Chemical Physics Theroy Group, Department of Chemistry
Flux dependent effects in degenerate and symmetric quantum
doubledot AharonovBohm interferometer
Coauthors: Malay Bandyopadhyay, Department of Physics, Indian
Institute of Technology, Bhubaneshwar India, Dvira Segal,
University of Toronto, Chemical Physics Theory Group, Department
of Chemistry
We study the steadystate characteristics and the transient
behaviour of the non equilibrium doubledot AharonovBohm
interferometer using analytical tools and numerically exact
influence functional path integrals. Our simple setup includes
non interacting degenerate quantum dots that are coupled
to two biased metallic leads at the same strength. A magnetic
flux pierces the interferometer perpendicularly. As we tune
the degenerate dot energies away from the symmetric point
we observe four nontrivial magnetic flux control effects:
(i) flux dependency of the occupation of the dots, (ii)
magnetic flux induced occupation difference between the
dots, at degeneracy, (iii) the effect of phaselocalization
of the dots coherence holds only at the symmetric point,
while in general both real and imaginary parts of the coherence
are nonzero, and (iv) coherent evolution survives even
when the dephasing strength, introduced via Büttiker
probes, is large and comparable to the dots energies and
the bias voltage. In fact, finite elastic dephasing can
actually introduce new types of coherent oscillations into
the systems dynamics. These four phenomena take place when
the dots energies are gated, to be positioned away from
the symmetric point, demonstrating that the combination
of bias voltage, magnetic flux and gating field, can provide
delicate control over the occupation of each of the quantum
dots, and their coherence.
Juan David Botero Instituto de
Física, Universidad de Antioquia, Medellín, Colombia
On the Dynamics of Spin1/2 particles: A Phasespace Pathintegral
Approach
Coauthors: Leonardo A. Pachón
The twolevel quantum system is the most fundamental element
in quantuminformationprocessing theory (QIPT) and one
of its more natural physical implementations comprises a
spin1/2system. Entangling these systems and their subsequence
manipulation, base on the nonlocal character of quantum
correlations, are the most fundamental protocols in QIPT.
The nonlocality that is exploited in those protocols is
a nonlocality between quantum systems; however, in order
to get a complete picture of the quantum correlations, one
has to analyze the influence of the nonlocal character
of the quantum dynamics itself (dynamical nonlocality).
We use the proposal given by Bjork et al [1] to construct
the Wigner function in a discrete phase space, then with
the aim to analize the dynamics of the of the spin1/2 particles,
we develop a formula for the discrete Wigner propagator
and calculate it by means of a direct method based on the
path integral formalism for discrete systems[2]. Having
already the explicit form for the Wigner propagator, we
can see explicitly the nonlocal behavior of the quantum
dynamics for the discrete systems.
[1] G. Björk, A. Klimov, L. SánchezSoto. Progress in Optics,
51, 496 (2008)
[2] L.S. Schulman. Techniques and applications of path integration.
Wileyinterscience publication. 1Ed (1996)
Aharon Brodutch IQC, University
of Waterloo
Restricted, distributed quantum gates
Coauthors:
The role of entanglement in quantum algorithms is somewhat
challenged by the existence of mixed state algorithms
that generate very little entanglement [1]. Moreover it
not clear if any other property of quantum states can
account for the source behind the quantum advantage [2].
A different candidate for this source is quantum gates
or more generally quantum operations. In this case entanglement
can be brought into the picture by considering distributed
implementations. To minimize resources it is useful to
take into account only the relevant set of input states
and simplify the gate's distributed implantation [3,4].
Using this approach we can identify the need for entanglement
resources as a function of the input/output sets. This
lets us make meaningful statements about the 'quantumness'
of various mixed state algorithms.
[1] Laflamme, R., D. G. Cory, C. Negrevergne, and L. Viola,
2002, Quantum Inf. Comput. 2, 166
[2] Vedral, V., 2010, Found. Phys. 40, 1141.
[3] Brodutch, A., and D. R. Terno, 2011, Phys. Rev. A
83, 010301.
[4] Brodutch, A., arXiv:1207.5105
Zhu Cao Center for Quantum Information,
Institute for Interdisciplinary Information Sciences, Tsinghua
University, Beijing 100084 China
Efficient Synchronization Scheme for Quantum Communication
Coauthors: HaiLin Yong, YanLin Tang, WeiYue Liu, DongDong
Li, ChengZhi Peng
Quantum key distribution (QKD) is the first practical
application in quantum information science. Time synchronization
technology plays an important role in QKD implementations.
In this field, the synchronization precision is required
to be in the subnanosecond regime, while the accuracy
of the current GPS system is in the order of a few nanoseconds.
To fill this gap, we propose an effective synchronization
algorithm, where we calibrate the frequency difference
and the offset between two remote clocks using internal
correlation between quantum signals. More specifically,
the frequency difference is derived by the ratio between
the transmitter's and receiver's internal clock time lengths
within a large number of GPS signals. Then the offset
is figured by fitting an optimal offset to maximize the
raw key rate. With the frequency difference and the offset
calibrated, we achieve a subnanosecondprecision synchronization.
With our synchronization algorithm, we complete two
QKD field tests. In our freespace 32 km decoystate QKD
experiment test, we manage to substantially improve the
synchronization precision, comparing to the conventional
hardwarebased synchronization scheme. As a result, we
are able to decrease the error rate and increase the raw
key rate. Results from another test, where the transmitter
is set in a moving vehicle, show that our synchronization
scheme is robust under harsh conditions. These two tests
demonstrate that our scheme can be useful for future global
highspeed QKD with a LEO satellite. Finally we remark
that our scheme may also be valuable for other quantum
communication applications, such as teleportation.
Aurelia Chenu Department of Chemistry
and Center for Quantum Information and Quantum Control, 80
Saint George Street, University of Toronto, Toronto, Ontario,
M5S 3H6 Canada
Sunlight can not be viewed as a series of random ultrafast
pulses
Coauthors: Agata M. Branczyk1, Greg D. Scholes1, and John
Sipe2 1 Department of Chemistry and Center for Quantum Information
and Quantum Control, 80 Saint George Street,University of
Toronto, Toronto, Ontario, M5S 3H6 Canada 2 Department of
Physics, 60 Saint George Street, University of Toronto, Toronto,
Ontario, M5R 3C3 Canada
Dynamics of energy transfer in photosynthetic
complexes occurs on a femtosecond (fs) time scale. It can
be resolved with ultrafast nonlinear spectroscopy [1],
where coherent fs pulses are being used to excite the molecular
systems. This is in contrast with natural excitation conditions
given by almost continuous and fully incoherent light from
the sun. In an attempt to make connections between the experimental
results using 2D electronic spectroscopy and the biological
processes occurring in photosynthetic organisms under natural
conditions, it has been suggested that sunlight can be viewed
as a series of random ultrafast pulses, with a duration
as short as the bandwidth allows [2].
To investigate this proposal, we construct a quantum state
of light composed of an incoherent mixture of multimode
coherent states. In the attempt to fit the properties of
thermal light, we show that the radiation spectrum and the
photon statistics can be well represented by a mixture of
pulses, as long as their spectral bandwidth is narrow enough
(>ps pulses). However, no physical solution can be found
for fs pulses, for which the bandwidth is comparable to
that of thermal light. Going to the secondorder correlation
function and the simultaneous excitation of two atoms, any
mixture of pulses is expected to fail in representing excitation
by thermal light in general.
References:
[1] E. Collini et al., Nature, 463, 644 (2010).
[2] Y.C. Cheng & G.R. Fleming, Annu. Rev. Phys. Chem.,
60, 241 (2009).
Greg Dmochowski University
of Toronto, Department of Physics
Increasing The Giant Kerr Effect By Narrowing The EIT Window
Beyond The Signal Bandwidth
Coauthors: Amir Feizpour, Matin Hallaji, Chao Zhuang, Alex
Hayat, Aephraim Steinberg
We experimentally show that EITbased Kerr nonlinearities
continue to benefit from narrowing the EIT window even as
the signal bandwidth comes to exceed this transparency width.
While previous studies have shown that narrow transparency
windows yield slow stepresponse times, thereby suggesting
a limitation of EITenhanced nonlinearities, our results show
that many practical applications of such nonlinearities, which
rely on pulsed fields, are not hindered by these effects.
In fact, these slow dynamics are at the root of the enhancement
offered by EIT in the regime of most interest, namely, narrow
EIT windows combined with high intensity, broadband signal
pulses. For applications such as quantum nondemolition measurements
and nonlinear optical gates where the goal is simply to detect
an observable singleshot phase shift, we see that EIT can
be used to increase the signal size even for broadband signal
pulses.
Amir Feizpour University of
Toronto
Weakvalue Amplification of Lowlightlevel Cross Phase
Modulation
Coauthors: Greg Dmochowski, Matin Hallaji, Chao Zhuang, Alex
Hayat, Aephraim M. Steinberg
We report on our experimental progress towards observing
weakvalue amplification of lowlightlevel crossphase modulation.
This will be the first observation of a weak measurement relying
on true entanglement between distinct systems which has no
classical interpretations, unlike previous weak measurement
experiments. In this scheme, classical pulses at singlephoton
level are sent to an interferometer one arm of which is interacting
with a probe pulse through a crossKerr effect. Postselecting
on having m photons in the dark port of the interferometer
results in an amplified m photon cross phase shift.
Kent Fisher Institute for Quantum
Computing, University of Waterloo
Quantum computing on encrypted data
Coauthors: Anne Broadbent, L. Krister Shalm, Zhizhong Yan,
Jonathan Lavoie, Robert Prevedel, Thomas Jennewein, Kevin
Resch
Performing computations on encrypted data is of strong significance
for protecting privacy over public networks. Such capabilities
would allow a client with a weak computer to send sensitive
data to a more powerful,but untrusted, server to be processed.
Recent works, called fully homomorphic encryption schemes,
have produced a long soughtafter solution to the problem
of carrying out classical computations on encrypted data.
Here we present an efficient solution to the quantum analogue
of this problem, allowing arbitrary quantum computations to
be carried out on encrypted quantum data. We prove that an
untrusted server can carry out a universal set of quantum
gates on encrypted qubits without learning any information
about the inputs while the client, who knows the decryption
key, can easily obtain the computed results. We experimentally
demonstrate, using single photons and linear optics, the encryption
and decryption scheme for each quantum gate in a set sufficient
for arbitrary quantum computations. Our protocol can be easily
incorporated into the design of quantum servers with few extra
resources. This result paves the way for delegated quantum
computing to take place, ensuring the privacy and security
of future quantum networks.
Roohollah (Farid) Ghobadi Institute
for Quantum Science and Technology, University of Calgary
Creating and detecting micromacro photonnumber entanglement
Coauthors: Alexander Lvovsky and Christoph Simon
We propose a scheme for the observation of micromacro entanglement
in photon number based on amplifying and deamplifying a singlephoton
entangled state in combination with homodyne quantum state
tomography. The created micromacro entangled state, which
exists between the amplification and deamplification steps,
is a superposition of two components with mean photon numbers
that differ by approximately a factor of three. We show that
for reasonable values of photon loss it should be possible
to detect micromacro photonnumber entanglement where the
macro system has a mean number of one hundred photons or more.
Gilad Gour Department of Mathematics
and Statistics, IQST, University of Calgary
Universal Uncertainty Relations
Coauthors: Shmuel Friedland, Vlad Gheorghiu
Uncertainty relations are a distinctive characteristic of
quantum theory that imposes intrinsic limitations on the precision
with which physical properties can be simultaneously determined.
The modern work on uncertainty relations employs entropic
measures to quantify the lack of knowledge associated with
measuring noncommuting observables. However, I will show
here that there is no fundamental reason for using entropies
as quantifiers; in fact, any functional relation that characterizes
the uncertainty of the measurement outcomes can be used to
define an uncertainty relation. Starting from a simple assumption
that any measure of uncertainty is nondecreasing under mere
relabeling of the measurement outcomes, I will show that Schurconcave
functions are the most general uncertainty quantifiers. I
will then introduce a novel finegrained uncertainty relation
written in terms of a majorization relation, which generates
an infinite family of distinct scalar uncertainty relations
via the application of arbitrary measures of uncertainty.
This infinite family of uncertainty relations includes all
the known entropic uncertainty relations, but is not limited
to them. In this sense, the relation is universally valid
and captures the essence of the uncertainty principle in quantum
theory.
Horacio Grinberg Department
of Physics, FCEyN, University of Buenos Aires, and IFIBA,
Argentina
Nonclassical effects in highly nonlinear twolevel spin
models
Coauthors:
The nonclassical squeezing effect emerging from a nonlienar
coupling model (generalized JaynesCummings model) of a
twolevel atom interacting with a bimodal cavity field via
twophoton transitions is investigated in the rotating wave
approximation. Various Bloch coherent initial states (rotated
states) for the atomic sysem are assumed. Initially the
atomic system and the field are in disentangled state, where
the field modes are in Glauber coherent states via Poisson
distribution. The model is numerically tested against simulations
of time evolution of the based Heisenberg uncertainty variance
and Shannon information entropy squeezng factors. The quantum
state purity is computed and used as a criterion to get
information about the entanglement of the components of
the system. Analytical expression of the total density operator
matrix elements at t > 0 shows in fact, the present
nonlinear model to be strongly entangled, where each of
the definite initial Bloch coherent states are reduced to
statistical mixtures. Thus, the present model does not preserve
the modulus of the Bloch vector.
Timur Grinev Chemical Physics
Theory Group, Department of Chemistry, and Center for Quantum
Information and Quantum Control, University of Toronto, Toronto,
Ontario M5S 3H6, Canada
Coherent control and incoherent excitation dynamics of
pyrazine
Coauthors: Paul Brumer
First, we present coherent control of internal conversion
(IC) between the S_1 and S_2 singlet excited electronic states
in pyrazine. S_2 state is populated from S_0 singlet state
in the process of weak field excitation. Coherent control
with respect to certain control objective is performed by
shaping the exciting laser. Excitation and IC are considered
simultaneously. Successful control is demonstrated by optimizing
both the amplitude and phase profiles of the laser, and its
dependence on the properties of S_2 resonances is established.
Second, we present the S_0 > S_2/S_1 photoexcitation
dynamics of pyrazine due to weak incoherent CW light excitation
after sudden turnon of the light. Dynamical evolution of
S_2 and S_1 populations, as well as the purity of the excited
mixed state, is studied. It is shown, that the S_1 to S_2
populations ratio becomes constant in the long time regime,
thus being an evidence of the spatially distributed nature
of the resulting excited mixed state. At the same time, the
excited mixed state purity decreases monotonically, but nonuniformly,
to a small asymptotic value (which is still restricted in
value by the purity of the maximally mixed state).
Andres Estrada Guerra Universidad
de Antioquia
NonMarkovian effects in the dynamics of entanglement in
high temperature limit
Coauthors: Leonardo Pachon Contreras
In the past years, some quantum phenomena have been observed
at macroscopic scales. In particular, superconductivity, coherent
superpositions of BoseEinstein condensates and interference
patterns in fullerenes have been detected. This fact has made
that the border between the quantum and classical realms become
more diffuse and intricate, although, more interesting, than
before.
However, in order to observe these quantum features, one
needs to reach the low temperature regime, E/(k_{B}T),
where E denotes a characteristic system energyscale and k_{B}T
the thermal energy. Therefore, some delicate and elaborate
cooling processes have been developed.
Our work aims to show that, even in the the high temperature
regime, some quantum features such entanglement can be present,
if the system is placed out from equilibrium. In particular,
we study the nonMarkovian dynamic of two different harmonic
oscillators coupled to different baths at different temperatures
and with different couplingtothebathstrengths. We found
that, despite the absence of symmetries in the parameters
space, entanglement between the oscillators can be created
and maintained in the longtime regime. We also discuss the
implementation of our setup for studying the influence of
the nonMarkovian dynamics in the optimal sideband cooling
of nanomechanical resonators.
Matin Hallaji Physics Department,
University of Toronto
Quantum control of population transfer between vibrational
states in an optical lattice
Coauthors: Chao Zhuang, Alex Hayat, and Aephraim M. Steinberg
We experiment on two quantum control techniques, Adiabatic
Rapid Passage (ARP) and Gradient Ascent Pulse Engineering
(GRAPE), to realize population transfer between vibrational
states of atoms trapped in an optical lattice. The ARP pulse
gives the highest population transfer among all the techniques
we have tested so far: 38.9±0.2 of the initial ground state
population is transferred into the first excited state, which
exceeds the 1/e boundary of coupling the ground and the first
excited vibrational states in a harmonic oscillator potential.
The ARP pulse also gives the highest normalized population
inversion among all the techniques we have tested so far:
the highest ratio of the difference between the ground state
and the first excited state population to the sum of the ground
state and the first excited state population is 0.21±0.02.
For the GRAPE technique, we use the GRAPE algorithm to engineer
a pulse involving both the displacement of the optical lattice
and modulation of the lattice depth, while the fidelity between
the state after the pulse is applied and the first excited
state is taken as the figure of merit. The GRAPE pulse gives
as high population transfer as the ARP pulse does: 39 ± 2
of the initial ground state population is transferred into
the first excited state. The GRAPE pulse outperforms the ARP
pulse if the leakage is concerned. Because the GRAPE pulse
gives almost no leakage compared to the 18.7 ± 0.3 leakage
for the ARP pulse, when the highest population transfer occurs.
Wolfram Helwig University of
Toronto
Absolutely Maximal Entanglement and Quantum Secret Sharing
Coauthors: Wei Cui, José Ignacio Latorre, Arnau Riera,
HoiKwong Lo
We study the existence of absolutely maximally entangled
(AME) states in quantum mechanics and its applications to
quantum information. AME states are characterized by being
maximally entangled for all bipartitions of the system and
exhibit genuine multipartite entanglement. We show that these
states exist for any number of parties if the system dimension
is chosen appropriately, and that they can be conveniently
described within the graph states formalism for qudits.
With such states, we present a novel parallel teleportation
protocol which teleports multiple quantum states between groups
of senders and receivers. The notable features of this protocol
are that (i) the partition into senders and receivers
can be chosen after the state has been distributed, and (ii)
one group has to perform joint quantum operations while the
parties of the other group only have to act locally on their
system. We also prove the equivalence between pure state quantum
secret sharing schemes and AME states with an even number
of parties.
Rolf Horn University of Waterloo,
Institute for Quantum Computing
On chip generation of polarization entanglement in a monolithic
semiconductor waveguide
Coauthors: Piotr Kolenderski, Dongpeng Kang, Payam Abolghasem,
Carmelo Scarcella, Adriano Della Frera, Alberto Tosi, Lukas
G. Helt, Sergei V. Zhukovsky, John E. Sipe, Gregor Weihs,
Amr S. Helmy, Thomas Jennewein
From unraveling the mysteries of the quantum world, to solving
really hard problems, a quest of those in the quantum information
community is to discover a technology that will facilitate
large scale implementations of quantum processes. In photonics,
the quest starts with finding a stable and scalable source
of single and entangled photons  the building blocks of
a photonic quantum computer. Here we present the Bragg Reflection
Waveguide (BRW), a tiny, stable and scalable semiconductor
waveguide, capable of directly producing polarization entangled
photons. It's design is perhaps the most truly monolithic
of any photon source available today;  the architecture
on which it is built promises electrical self pumping, and
in contrast to many other nonlinear optics type sources,
nothing is required to create entanglement but the device
itself. To demonstrate this, we examine the photon pairs produced
via Spontaneous Parametric Down Conversion in a 2.2mm long,
3.8 micron wide BRW. We perform quantum state tomography on
the photon pairs, splitting them immediately after they emerge
from the chip, and show their significant departure from classical
behaviour. Solidified via the observation of their spectra,
we calculate a concurrence of approximately 0.5, demonstrate
polarization entanglement visibilities from 64% to 96% in
various basis, and determine the fidelity with a maximally
entangled state to be 0.83. Combined with the BRW's truly
monolithic architecture these results signify the BRW chip
architecture as a serious contender on which to build large
scale implementations of optical quantum processes.
Nathaniel Johnston Institute
for Quantum Computing, University of Waterloo
On the Minimum Size of Unextendible Product Bases
Coauthors: Jianxin Chen
A longstanding open question asks for the minimum number
of vectors needed to form an unextendible product basis
in a given bipartite or multipartite Hilbert space. A solution
to this problem has applications to the construction of
bound entangled states and Bell inequalities with no quantum
violation. A partial solution was found by Alon and Lovasz
in 2001, but since then only a few other cases have been
solved. We solve all remaining bipartite cases (i.e., where
there are only 2 subsystems), all remaining qubit cases
(i.e., where each local dimension is 2), as well as many
other multipartite cases.
Dongpeng Kang Department of Electrical
& Computer Engineering, University of Toronto
Bragg reflection waveguides: The platform for monolithic
quantum optics in semiconductors
Coauthors: Amr S. Helmy
Photon pairs are one of the most important and widely used
nonclassical states of light in quantum optics. They are
indispensible sources in various applications in domains
such as quantum key distribution, optical quantum computing,
amongst others. One of the more popular methods to generate
photon pairs is via spontaneous parametric downconversion,
which requires a laser source pumping a nonlinear crystal
in a specific set of configurations. The system is generally
bulky, vulnerable, and sensitive to the external environment,
therefore it’s useful in specially equipped labs. On the
other hand, a mobile and commercially viable quantum information
processing system, such as an optical quantum computer,
requires chipscale, portable, robust sources of photon
pairs operating at room temperature. Although significant
progress has been made using different techniques, electrically
pumped, roomtemperature photon pairs are still unavailable.
To this end, Bragg reflection waveguides (BRWs) made of
IIIV semiconductors such as Aluminum Gallium Arsenide have
been shown as the most promising platform to realize this
class of sources. Efficient photon pair generation as well
as polarization entanglement have been demonstrated in BRWs.
In this work, we first review BRWs as a platform for phase
matching in isotropic and highly dispersive semiconductors.
We will show dispersion and birefringence engineering can
be employed to tailor the properties of the photon pairs,
for example, to generate polarization entangled photons onchip
without any offchip compensation or interferometry. Our results,
combined with its truly monolithic nature, show that BRWs
could lead to fully integrated nonclassical photon sources.
Eric Kopp University of Toronto
New Control Frontiers in Noiseless Subspaces
Coauthors:
Quantum control is largely divided into two independent
problems: control for the purpose of protecting information
and preventing decoherence, and control for the purpose
of manipulating states to accomplish computational goals.
Achieving both control objectives simultaneously is a formidable
task and has typically only been addressed for specific
lowdimensional systems. Our research examines control strategies
for realizing a universal set of operations (gates) while
confining states to noiseless subspaces in systems of 4
qubits and greater. These strategies are applicable to a
broad class of models and control inputs. Aspects of the
research focus on recasting a specific class of noiseless
subspace into a classical problem in geometric control,
and addressing the computational challenges in working with
extremely large, extremely sparse tensor operator representations
in an efficient way. Preliminary results will also be shown
for a 4qubit 'representative' trapped ion model with a
realistic experimental setup.
Hoi Kwan Lau University of Toronto
Rapid laserfree ion cooling by controlled collision
Coauthors:
I propose a method to transfer the axial motional excitation
of a hot ion to a coolant ion with possibly different mass
by precisely controlling the ion separation and the local
trapping potentials during ion collision. The whole cooling
process can be conducted diabatically, involving only a
few oscillation periods of the harmonic trap. With sufficient
coolant ions preprepared, this method can rapidly recool
ion qubits in quantum information processing without applying
lengthy laser cooling.
Hoi Kwan Lau University of Toronto
Quantum secret sharing with continuous variable cluster
states
Coauthors: Christian Weedbrook
We extend the idea of cluster state quantum secret sharing
to the continuous variable regime. Both classical and quantum
information can be shared by distributing finitely squeezed
continuous variable cluster states through either secure
or insecure channels. We show that the security key rate
of the classical information sharing can be obtained by
standard continuous variable quantum key distribution techniques.
We analyse the performance of quantum state sharing by computing
the shared entanglement of between the authorised parties
and the dealer. Our techniques can be applied to analyse
the security of general continuous variable quantum secret
sharing.
Xiongfeng Ma Tsinghua University
Experimental realization of measurementdeviceindependent
quantum key distribution
Coauthors: Yang Liu, TengYun Chen, LiuJun Wang, Hao Liang,
GuoLiang Shentu, Jian Wang, Ke Cui, HuaLei Yin, NaiLe Liu,
Li Li, Jason S. Pelc, M. M. Fejer, ChengZhi Peng, Qiang Zhang,
and JianWei Pan
Throughout history, every advance in encryption has been
defeated by advances in hacking, often with severe consequences.
Quantum cryptography [1] holds the promise to end this battle
by offering unconditional security when ideal singlephoton
sources and detectors are employed. Unfortunately, ideal
devices never exist in practice and device imperfections
have become the targets of various attacks. By developing
upconversion singlephoton detectors with high efficiency
and low noise, we faithfully demonstrate the measurementdeviceindependent
quantum key distribution (MDIQKD) protocol [2], which is
immune to all hacking strategies on detection. Meanwhile,
we employ the decoystate method [3] to defend attacks on
nonideal source. By assuming a trusted source scenario,
our practical system, which generates more than 25 kbits
secure key over a 50 km fiber link, serves as a step stone
in the quest for unconditionally secure communications with
realistic devices.
The gap between ideal devices and realistic setups has been
the root of various security loopholes [4], which have become
the targets of many attacks [5,6]. Tremendous efforts have
been made towards loopholefree QKD with practical devices
[7,8]. However, the question of whether security loopholes
will ever be exhausted and closed still remains. Here, we
report a QKD experiment that closes the loopholes in detection
and hence can achieve secure communication in a trusted
source scenario. Firstly, ideal singlephoton sources are
replaced with weak coherent states by varying mean photon
intensities, a technique called decoystate method [3].
Secondly, by implementing the recently developed MDIQKD
protocol [2], all the detection side channels are removed
from our system.
[1]. C. H. Bennett and G. Brassard, in Proceedings of the
IEEE International Conference on Computers, Systems and
Signal Processing (IEEE Press, New York, 1984) pp. 175179.
[2]. H.K. Lo, M. Curty, and B. Qi, Phys. Rev. Lett. 108,
130503 (2012).
[3]. H.K. Lo, X. Ma, and K. Chen, Phys. Rev. Lett. 94,
230504 (2005).
[4]. D. Gottesman, H.K. Lo, N. Lutkenhaus, and J. Preskill,
Quantum Inf. Comput. 4, 325 (2004).
[5]. V. Makarov, A. Anisimov, and J. Skaar,Phys. Rev. A
74, 022313 (2006).
[6]. B. Qi, C.H. F. Fung, H.K. Lo, and X. Ma, Quantum
Inf. Comput. 7, 073 (2007).
[7]. D. Mayers and A. Yao, in FOCS, 39th Annual Symposium
on Foundations of Computer Science (IEEE, Computer Society
Press, Los Alamitos, 1998), p. 503.
[8]. A. Acin, N. Gisin, and L. Masanes, Phys. Rev. Lett.
97, 120405 (2006).
Dylan Mahler University of Toronto,
Adaptive quantum state tomography improves accuracy quadratically
Coauthors: Lee A. Rozema, Ardavan Darabi, Chris Ferrie, Robin
BlumeKohout, and A.M. Steinberg
In quantum state tomography, an informationally complete
set of measurements is made on N identically prepared quantum
systems and from these measurements the quantum state can
be determined. In the limit as N → ∞, the estimate
of the state converges on the true state. The rate at which
this convergence occurs depends on both the state and the
measurements used to probe the state. On the one hand, since
nothing is known a priori about the state being probed,
a set of maximally unbiased measurements should be made.
On the other hand, if something was known about the state
being measured a set of biased measurements would yield
a more accurate estimate. It has been shown[1, 2] that by
adaptively choosing measurements, optimal accuracy in the
state estimate can be obtained regardless of the state being
measured. Here we present an experimental demonstration
of one and twoqubit adaptive tomography that achieves
a rate of convergence of approximately 1O([1/N]) in the
quantum state fidelity with only a single adaptive step
and local measurements, as compared to 1O([1/(√(N))])
for standard tomography. [1] Phys. Rev. Lett. 97, 130501
(2006) [2] Phys. Rev. A 85, 052120 (2012)
Sebastian Duque Mesa
Relativistic Dynamical Quantum Nonlocality
Coauthors: Leonardo A. Pachon
In nonrelativistic quantum mechanics, quantum correlations
are largely thought to be absolute. However, when they are
studied in the framework of relativistic quantum mechanics
they could depend on the reference frame [1]. In particular,
two particles could be entangled in one reference frame
but unentangled in another one, thus quantum nonlocality
depends upon the reference frame.
Here, the nonlocality of quantum dynamics was tracked,
by working to the Weyl’s representation of quantum mechanics,
to the superposition principle. This is a kind of single
particle nonlocality, of different nature as the discussed
above [2]. We extend this work to the relativistic framework
of quantum mechanics. To do so, we review the basics of
the relativistic Weyl’s formalism and discuss the construction
of the pathintegral representation of the Wigner function,
as well as the influence of the reference frame on this
dynamical quantum nonlocality.
References:
[1] Robert M. Gingrich and Christoph Adami. Quantum entanglement
of moving bodies. Phys. Rev. Lett., 89:270402, Dec 2002.
[2] S. Popescu. Dynamical quantum nonlocality. Nature Phys.,
6:151, 2010.
Leonardo A. Pachon Department
of Chemistry, University of Toronto
Coherent Phase Control in Closed and Open Quantum Systems
Coauthors: Paul Brumer
The underlying mechanisms for one photon phase control
are revealed through a master equation approach and based
on the path integral approach in the energy basis representation.
Specifically, two mechanisms are identified, one operating
on the laser time scale and the other on the time scale
of the systembath interaction. The effect of the secular
and nonsecular Markovian approximations are carefully examined.
We discuss the possibility of enhancing this environmentassisted
effect when a description based on subOhmic spectral densities
applies.
Kyungdeock Park (Daniel) Institute
for Quantum Computing
Heat Bath Algorithmic Cooling and Multiple Rounds Quantum
Error Correction Using Nuclear and Electron Spins
Coauthors: Robabeh Darabad, Ben Criger, Jonathan Baugh and
Raymond Laflamme
Nuclear Magnetic Resonance (NMR)based devices have been
excellent test beds for Quantum Information Processing (QIP).
However, the spin polarization bias in a typical experimental
setup is very small at thermal equilibrium, giving a highly
mixed qubit, and the polarization decreases exponentially
in the number of qubits. Thus it is very difficult to have
closetopure ancilla qubits which are essential in the
implementation of quantum error correction (QEC). Moreover,
for practically stable systems against noise, QEC should
be performed multiple rounds. This requires ancilla qubits
to be refreshed at the initial stage of each round to very
high polarization. In order to accomplish this in NMR QEC
experiment, we seek to implement Heat Bath Algorithmic Cooling
(HBAC) with cold electron spin bath. HBAC is an implementation
independent cooling method that combines reversible entropy
compression and interaction with the cold external bath.
It is capable of cooling a qubit of interest far beyond
the bath polarization. Electron spins possess higher polarization
and faster relaxation rate than nuclear spins under similar
experimental conditions, and thus can be used as the heat
bath while nuclear spins encode system qubits. In this talk,
I will present our progress towards achieving high polarization
of nuclear spin qubits using an electron spin and HBAC.
In addition, I will show how this will be used in future
for the experimental realization of multiple rounds of threequbit
QEC.
Alexandru Paler University of
Passau
Resource Optimization in Topological Quantum Computation:
Verification.
Coauthors: Simon Devitt*, Kae Nemoto*, Ilia Polian+; * National
Institute of Informatics, Tokyo, Japan; + University of Passau,
Passau, Germany;
Recent advances in large scale quantum architecture design
has focused on utilizing topological codes to perform necessary
error correction protocols. These codes use a geometric
description to specify quantum circuits in terms of topological
braiding. Recent results have introduced several techniques
to optimize topological circuits by compressing the overall
3dimensional volume of the circuit description which acts
to minimize the total number of physical qubits and the
total amount of computational time needed to realize a given
circuit [1].
These compression techniques have as yet only been implemented
manually, and on small topological circuits. Therefore,
it is reasonably straightforward to check that no mistakes
are made. Future classical programs and game based efforts
[2] that are used to compile and optimized topological circuits
will be automated and used to compress extremely large topological
structures. As with classical circuit designs, the output
of these automated protocols must be verified before accepted.
In this presentation we will outline the steps required
to verify topological quantum circuits. We will illustrate
several algorithmic steps that are required in order to
accurately check the function of optimized circuits without
having to directly simulate topological computation.
[1] A.G. Fowler and S.J. Devitt, arXiv:1209.0510
[2] www.qubitgame.com
Nicolas Quesada University of
Toronto
Selfcalibrating tomography for nonunitary processes
Coauthors: Agata M. Branczyk and Daniel F.V. James
Characterizing quantum states and processes is a key step
for many quantum information and quantum computing protocols
[1]. We extend upon the idea of using an incompletely characterized
process to perform quantum state tomographyknown as selfcalibrating
tomography [2,3]by including the possibility that the
process itself is not unitary. We study a two level atom,
with an unknown dipole moment, that undergoes spontaneous
emission and is irradiated by a laser whose phase and intensity
can be controlled at will. We show that by using five different
parameter settings of the electric field of the laser it
is possible to reconstruct the state as well as obtain the
unknown spontaneous emission rate and dipole moment of the
atomsimultaneously performing quantum state and quantum
process tomography.
References:
[1] M. A. Nielsen and I. L. Chuang, Quantum computation
and quantum information (Cambridge university press, 2010).
[2] A. Branczyk, D. H. Mahler, L. A. Rozema, A. Darabi,
A. M. Steinberg, and D. F. James, “Selfcalibrating quantum
state tomography,” New Journal of Physics 14, 085003 (2012).
[3] N. Quesada, A. M. Branczyk, and D. F. James, “Selfcalibrating
tomography for multidimensional systems,” arXiv preprint
arXiv:1212.0556 (2012).
Katja Ried Perimeter Institute
for Theoretical Physics
Quantum process tomography with initial correlations
Coauthors: Robert W. Spekkens
When preparing input states for quantum process tomography
(QPT), one may face undesired correlations between the system
and environment degrees of freedom. In this case the results
obtained by the standard QPT scheme may not characterize
the process in question accurately. Instead, the data may
reflect properties of the joint initial state of system
and environment, as one would expect in quantum state tomography
(QST). We present a unified framework for QPT and QST that
can handle this scenario and report on progress in distinguishing
the “processtype” from the “statetype” contributions in
data from this tomography.
Christoph Reinhardt McGill
University
Design of a Strong Optomechanical Trap
Coauthors: Simon Bernard, Jack Sankey
We report progress toward an optomechanical setup in which
a partiallyreflective micromechanical element is positioned
within an optical cavity formed by two rigidlyfixed mirrors.
This threemirror system provides a highly versatile platform
for studying new optomechanical effects; in particular,
it is possible to generate a nonlinear coupling in which
the cavity resonance varies quadratically as a function
of mechanical displacement, enabling (among other things)
a strong cavity optical trap. We fabricate our mechanical
elements by patterning freestanding silicon nitride membranes
into lightweight, weaklytethered “trampolines”
so that a strong optical trap can completely dominate over
the forces exerted by the supporting material. Such systems
are predicted to achieve extraordinarily high mechanical
quality factors, and our ultimate goal is to use them to
sense incredibly small forces, such as those exerted by
quantum systems prepared in superposition states.
Lee Rozema University of Toronto
Experimental Demonstration of Quantum Data Compression
Coauthors: Dylan H. Mahler, Alex Hayat, Peter S. Turner, and
Aephraim M. Steinberg
In quantum state tomography N identically prepared copies
of a quantum state are measured to reconstruct a density
matrix describing the single particle state. One purpose
of reconstructing a density matrix is to allow the prediction
of measurements that could have been made on the initial
state. On the other hand, if only one measurement is of
interest then performing that measurement on the each of
the N copies of the state will yield the most accurate estimate.
However, if the measurement choice is unknown the quantum
states must be stored in a quantum memory until a later
time. The question then becomes: how much memory is required?
Hilbert space grows exponentially in the number of qubits.
The dimensionality of an N qubit system is 2^{N},
but if all of the qubits are identical the initial N qubit
state can be described by the symmetric subspace, which
has dimension N+1. Physically, the information of the initial
state can be mapped onto the first log_{2}(N+1)
qubits using the Quantum SchurWeyl transform (QSWT), leading
to an exponential savings in space.
Here, we present an experiment compressing three qubits
into two. In our experiment the three qubits are encoded
in two photons. The first photon encodes a path and a polarization
qubit, while the second photon encodes a single polarization
qubit. We use the QSWT to map all of the information from
the 3 qubits onto the path and polarization qubits encoded
in the first photon, allowing us to discard the second photon.
Lena Simine Chemical Physics
Theory Group, Dept. of Chemistry, University of Toronto
Numerical simulations of molecular conducting junction:
transport and stability
Coauthors: Dvira Segal
We present a computational study of a minimalistic molecular
conducting junction using a numerically exact path integral
method. The effects of bias induced vibrational instability
and mode equilibration with secondary phonon modes are investigated.
We also address the competition between direct tunneling
and phonon assisted transport, and look into thermoelectric
regime.The comparison of exact numerical simulations to
perturbative master equation results indicate on the importance
of high order electronphonon scattering processes.
Xin Song University of Toronto
Enhanced probing of fermionic interaction using weakvalue
amplification
Coauthors: Amir Feizpour, Yao Tian, Alex Hayat, Aephraim Steinberg
We demonstrate a scheme for enhanced probing of an interaction
between two single fermions by probing the spindependent
energy splitting of an excitonic system in semiconductor
quantum dots based on weakvalue amplification. Since both
spin and energy of the anisotropic electronhole exchange
interaction in quantum dots can be mapped to emitted photons,
we can use the polarization of these emitted photons to
initialize and postselect the system. By preparing and
postselecting the emitted photons into two quasiorthogonal
quantum polarization state i> and f>, which satisfies
<if> << 1, we are able to obtain an enhanced
outcome of the weak value <A>=<fAi>/<fi>,
which is proportional to the energy splitting of the excitonic
system. Weakvalue amplification provides an effective technique
for enhancedprecision measurement of fermion system when
considering the limitation due to slow noise.
Zhiyuan Tang University of Toronto
Experimental demonstration of polarization encoding measurementdeviceindependent
quantum key distribution
Coauthors: Zhongfa Liao, Feihu Xu, Bing Qi, Li Qian, HoiKwong
Lo
Measurementdeviceindependent quantum key distribution
(MDIQKD) has been proposed to close all the potential security
loopholes due to imperfections in the detectors without
compromising the performance of a standard QKD system [1].
Various experimental attempts on MDIQKD have been reported
in both timebin [2, 3] and polarization encoding [4]. We
remark that in [2, 4] only Bell state measurements with
different combinations of BB84 states and photon levels
are conducted, and thus no real MDIQKD (which requires
Alice and Bob randomly switch their qubits’ states and intensity
levels) is implemented. A complete timebin encoding MDIQKD
experiment has been reported in [3]. However, phase randomization,
a crucial assumption in the security of QKD, is neglected
in their experiment, which leaves the system vulnerable
to attacks on the imperfect weak coherent sources [5].
Here we report the first complete demonstration of polarization
encoding MDIQKD over 10 km optical fiber. Decoy state technique
is employed to estimate gain and error rate of single photon
signals. Photon levels and probability distributions for
the signal and decoy states are chosen numerically to optimize
the key rate. Active phase randomization is implemented
for the first time in MDIQKD to protect against attacks
on the imperfect sources. A 1600bit secure key is generated
in our experiment. Our experiment verifies the feasibility
to implement MDIQKD with polarization encoding.
[1] H. –K. Lo, M. Curty , and B. Qi, “MeasurementDeviceIndependent
Quantum Key Distribution,” Phys. Rev. Lett. 108, 130503
(2012).
[2] A. Rubenok, et al., “A Quantum Key Distribution Immune
to Detector Attacks,” arXiv: 1204.0738.
[3] Y. Liu, et al., “Experimental MeasurementDeviceIndependent
Quantum Key Distribution,” arXiv:1209.6178.
[4] T. Ferreira da Silva, et al., “ProofofPrincipe Demonstration
of Measurement Device Independent QKD Using Polarization
Qubits,” arXiv: 1207.6345.
[5] Y. Tang, et al., “Source Attack of Decoy State Quantum
Key Distribution Using Phase Information,” arXiv: 1304.2541.
Johan F. Triana Instituo de Física,
Universidad de Antioquia
The Quantum Limit at Thermal Equilibrium
Coauthors: Leonardo A. Pachón (Instituo de Física, Universidad
de Antioquia)
The aim of constructing and designing machines working
at the nanometrelength scale, such as atomic motors, photocells,
gyrators or heat engines, has boosted the developing of
a quantum version of thermodynamics. One of the foundational
conundra in this emerging field is, to what extent nanomachines
can display quantum features and how this quantum behaviour
could be used to improve their efficiency. Intuitively,
one can suggest that if the energy of the thermal fluctuations
is much smaller than the typical energy scale of the nanosystem,
then there is room for the nanosystem to revels its quantum
nature. However, as it has been discussed recently in almost
all fields related to quantum mechanics (e.g quantum information
science, quantum biophysics, nanotechnology, quantum chemsitry
or condensed matter physics), the border between the quantum/classical
operating regime is far from being trivial. We predict here,
at thermodynamical equilibrium, the existence of a regime
where, e.g., nanoelectromechanical structures or optomechanical
systems can be found in an entangled state at high temperature
assisted by the nonMarkovian interactions. Complementarily,
we report the existence of a second regime, characterized
by Markovian interactions at low temperature, where quantum
nanodevices do not thermalize into the canonical Boltzmann
distribution, and therefore all their thermodynamical properties
are expected to deviate, even, from current quantum thermodynamics.
Our findings not only provides a solid ground for understanding
the presence of quantum features in most of current investigations
in bio and handmade systems, but also points out the direction
to follow in protecting and isolating of quantum systems.
Timur Tscherbul Department
of Chemistry and Centre for Quantum Information and Quantum
Control, University of Toronto
Quantum coherent dynamics of Rydberg atoms driven by cold
blackbody radiation
Coauthors: Paul Brumer
The interaction of incoherent blackbody radiation with
atoms and molecules is usually considered in the framework
of Markovian rate equations parametrized by the Einstein
coefficients, leading to a linear increase of excitedstate
populations with time. While the validity of the rate equations
is justified by the extremely short coherence time of hot
blackbody radiation (2 ps at a temperature of 4100 K), deviations
from the linear behavior are expected on shorter time scales.
By solving perturbative equations of motion for the density
matrix of an atom interacting with a cold thermal reservoir
of radiation field modes, we obtain the dynamics of eigenstate
populations and coherences without invoking the Markovian
approximation. The theory is applied to examine the coherent
effects in highly excited Rydberg atoms subject to a cosmic
microwave background radiation.
X. Xing University of Toronto
Multidimensional quantum information based on temporal
photon modulation
Coauthors: A. Hayat, A. Feizpour, and A. M. Steinberg.
Multidimensional quantum information processing has been
shown to open a wide range of possibilities. The spatial
degree of freedom has been recently employed to encode multidimensional
quantum information using photon orbital angular momentum.
This approach, however, is not suitable for the singlemode
fiberoptical communication infrastructure. We demonstrate
experimentally a multidimensional quantum information encoding
approach based on temporal modulation of single photons,
where the Hilbert space can be spanned by an inprinciple
infinite set of orthonormal temporal profiles. We implement
the temporal encoding using a scheme where the projection
onto temporal modes is implemented by an electrooptical
modulator and a narrowband optical filter. The demonstrated
temporal multidimensional quantum encoding allows quantum
communication over existing fiber optical infrastructure,
as well as probing multidimensional time entanglement approaching
the limit of continuoustime measurements.
Zhen Zhang Tsinghua University
Decoystate quantum key distribution with biased basis
choice
Coauthors: Zhengchao Wei,Weilong Wang, Xiongfeng Ma
Quantum key distribution (QKD) plays an
important role in the field of Quantum Information. The
most wellknown QKD scheme is BB84 protocol [1], where a
single photon source is assumed. In reality, a perfect single
photon source does not exist. Instead, highly attenuated
lasers are widely used for QKD. The multiphoton component
in a laser source leads to a security threat (e.g., photon
number splitting attack [2]). The decoystate method is
proposed to address this issue by using more than one intensities
and its security has been proven by Lo, Ma, and Chen [3].
Meanwhile, in the original BB84, Alice encodes the key information
randomly into the X and Z bases with the same probability
and Bob measures the received qubits in two bases randomly
with equal probabilities. We denote the basissift factor
to be the ratio between the lengths of the sifted key and
the raw key. The basissift factor of the original BB84
protocol is 1/2. The efficient BB84 protocol proposed by
Lo, Chau and Ardehali [4], in which Alice and Bob put a
bias between the probabilities of choosing the Z and X bases,
can improve the basissift factor up to 100%.
In this work, we propose a QKD protocol that combines the
decoystate method with the efficient BB84 protocol. In
this scheme, Alice sends all signal states in the Z basis.
We optimize the probabilities of Alice sends decoy states,
signal states and vacuum states, the probabilities of the
X and Z bases in decoy state, the probabilities of the X
and Z bases Bob chooses for measure, and the intensity of
the decoy state. From the simulation result, after taking
into account of statistical fluctuations, our protocol can
improve the key rate by at least 45% comparing to the original
decoystate protocol.
[1] C. H. Bennett and G. Brassard, in Proceedings of the
IEEE International Conference on Computers, Systems and
Signal Processing (IEEE Press, New York, 1984) pp. 175179.
[2] G. Brassard, N. Lutkenhaus, T. Mor, and B. C. Sanders,
Phys. Rev. Lett. , 85, 1330 (2000).
[3] H.K. Lo, X. Ma, and K. Chen, Phys. Rev. Lett. 94,
230504 (2005).
[4] H.K. Lo, H. F. Chau , and M. Ardehali, Journal of
Cryptology 18, 133 (2005).
Tian Wang Institute for Quantum
Science and Technology, University of Calgary
Demonstrating macroscopic entanglement based on Kerr nonlinearities
requires extreme phase resolution
Coauthors: Roohollah Ghobadi, Sadegh Raeisi, Christoph Simon
Entangled coherent states, which can in principle be created
using strong Kerr nonlinearities, allow the violation of
Bell inequalities for very coarsegrained measurements.
This seems to contradict a recent conjecture that observing
quantum effects in macroscopic systems generally requires
very precise measurements. However, here we show that both
the creation of the required states and the required measurements
rely on being able to control the phase of the necessary
Kerrnonlinearity based unitary operations with extreme
precision. And the requirement for phase control increases
dramatically with increasing size of the cat state. This
lends support to the idea that there is a general principle
that makes macroscopic quantum effects difficult to observe,
even in the absence of decoherence.
Feihu Xu University of Toronto
Measurement Device Independent Quantum Key Distribution
in a Practical Setting
Coauthors: Marcos Curty, Bing Qi, Wei Cui, Charles Ci Wen
Lim, Kiyoshi Tamaki, and HoiKwong Lo
A groundbreaking scheme – measurement device independent
QKD (MDIQKD) [Phys. Rev. Lett. 108, 130503, 2012] – was
proposed to solve the “quantum hacking” problem. More precisely,
MDIQKD removes all attacks in the detection system, the
most important loophole of QKD implementations. It is highly
practical and can be implemented with standard optical components.
Very recently, MDIQKD has been demonstrated by a number
of research groups, but before it is applicable in real
life, it is important to resolve a number of practical issues.
In this paper, we solve the practical issues in the reallife
implementations of MDIQKD. Firstly, we study the physical
origins of the quantum bit error rate in reallife MDIQKD
by proposing general models for various practical errors.
Secondly, we present a rigorous method to study both the
finitedecoy protocol and the finitekey analysis. In the
finitekey analysis, we use the Chernoff bound to estimate
the statistical fluctuations and consider the smooth minentropy
formalism to analyze the finitekey effect. Finally, we
offer a general framework to evaluate the optimal choice
of intensities of signal and decoy states. Our result is
of particular interest both to researchers hoping to demonstrate
MDIQKD and to others performing nonQKD experiments involving
quantum interference.
Eric Zhu Department of Electrical
& Computer Engineering, University of Toronto
Broadband Polarization Entanglement Generation in a Poled
Fiber
Coauthors: Z. Tang, L. Qian, L.G. Helt, M. Liscidini, J.E.
Sipe, C. Corbari, P.G. Kazansky
In this paper, we will give an overview of our recent work
in poled twinhole fiber, fiber that has a nonzero secondorder
nonlinearity. Along with the intrinsic form birefringence
of the fiber, we have been able to exploit the typeII phasematched
parametric downconversion process to generate highfidelity
polarizationentangled photon pairs. We emphasize that this
generation of polarization entanglement is direct, without
the need for interferometric means or walkoff compensation.
The quality of our source is examined through a number of
characterization techniques, including twophoton interference,
HongOuMandel interference, and quantum state tomography.
Furthermore, the unique dispersion properties of the poled
fiber allow for broadband polarizationentanglement over
100 nm centered at 1550 nm, opening up our source to many
potential applications from highresolution quantum optical
coherence tomography, to wavelengthdivisionmultiplexed
schemes of distributing entangled photons to multiple biparties
for quantum cryptography and other exciting quantum technologies.
