Contributed
Talks Index 
 Paul
Barclay, Institute for Quantum Science and Technology,
University of Calgary
Nanoscale optomechanics for sensing and hybrid
quantum systems
 Martin
Bruderer Institute for Theoretical Physics, Ulm
University
Controlling and measuring quantum transport of
heat in trappedion crystals
 Alessandro
Cerè Center for Quantum Technologies, National
University of Singapore
Toward The Generation Of Bell Certified Randomness
Using Photons
 M.
Cramer Ulm University
Quantifying entanglement with simple measurements
 Keiichi
Edamatsu Research Institute of Electrical Communication,
Tohoku University
Experimental test of errordisturbance uncertainty
relations in generalized photonpolarization
measurements
 Nicolas
Gisin University of Geneva
Displacing entanglement back and forth between
the micro and macro domains
 Michael
Hall Centre for Quantum Dynamics, Griffith University
(Brisbane, Australia).
Experimental test of universal complementarity
relations
 Bas
Hensen Kavli Institute of Nanoscience Delft, Delft
University of Technology
Heralded entanglement between solidstate qubits
separated by 3 meters
 Khabat
Heshami Institute for Quantum Science and Technology,
University of Calgary
Raman optical quantum memory in NV ensembles coupled
to a cavity
 Holger
F. Hofmann Graduate School of Advanced Sciences
of matter, Hiroshima University,
Weak measurement statistics as fundamental law
of physics: How inequality violations originate from
deterministic relations between the properties of
a quantum system
 Gregory
A. Howland University of Rochester Department
of Physics and Astronomy
Imaging Spatial Entanglement with Compressive Sensing
 Chengyong
Hu Department of E & E, University of Bristol,
United Kingdom
Solidstate quantum communications and quantum
computation based on single quantumdot spin in optical
microcavities

 Gustavo
Lima Center for Optics and Photonics, MSINucleus
for Advanced Optics,
Departamento de Física, Universidad de Concepción,
Chile.
Long distance propagation of genuine energytime
entanglement.
 Jeff
Lundeen Physics Dept., University of Ottawa
Experimental measurement of a point in phasespace:
Observing Dirac's classical analog to the quantum
state
 Roee
Ozeri Weizmann Institute of Science
Active Decoherence Suppression methods in Metrology
 Marco
Piani Institute for Quantum Computing, University
of Waterloo
Entanglementbased uncertainty principle for sequential
measurements
 Sadegh
Raeisi Institute for Quantum Computing
High Polarization of Nuclear Spins by Modulating
a Coupled Electron Spin
 Paul
RaymondRobichaud Université de Montréal
Parallel Lives
 Jacquiline
Romero University of Glasgow
A nontrivial trivial detection loophole
 James
Schneeloch University of Rochester
EinsteinPodolskyRosen Steering Inequalities from
Entropic Uncertainty Relations
 Olga
Sminrova MaxBorn Institute
Attosecond Larmor clock
 Joshua
A. Slater Institute for Quantum Science and Technology,
University of Calgary,
An experimental test of all theories with predictive
power beyond quantum theory
 T.
H. Taminiau Delft University of Technology
Measurementbased entanglement and Bell inequality
violation with individual solidstate spins
 Harald
Weinfurter, Faculty of Physics, LudwigMaximiliansUniversity,
MaxPlanck
Institut for Quantum Optics,
Heralded entanglement between widely separated
atoms A route towards a loophole free test of Bell's
inequality ?
 Gerardo
Viza University of Rochester
Weakvalues technique for Velocity Measurements

Paul Barclay, Institute for
Quantum Science and Technology, University of Calgary
Nanoscale optomechanics for sensing and hybrid quantum
systems
Recent advances in optomechanics utilize the colocalization
of optical and mechanical modes for coherent energy exchange
between photons and phonons within nanoscale structures.
These optomechanical devices have demonstrated exceptional
promise as sensors of mechanical motion, and as probes of
mesoscopic quantum effects. We have recently demonstrated
optomechanical devices optimized for detecting torsional
forces associated with nanoelectronic and magnetic systems.
These devices are created from "split beam" photonic
crystal nanocavities, which allow optical coupling to a
variety of torsional and cantilever mechanical modes. They
are characterized by single phonon optomechanical coupling
rates close to a MHz, sub pg masses, and frequencies ranging
from 5  20MHz. Ongoing studies are focused on using these
devices for sensing, and for creating hybrid quantum systems
coupling quantum optical, electronic and mechanical degrees
of freedom.
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Martin Bruderer Institute for
Theoretical Physics, Ulm University, AlbertEinstein
Allee 11, 89069 Ulm, Germany
Coauthors: Alejandro Bermudez, Martin B. Plenio
Controlling and measuring quantum transport of heat
in trappedion crystals
Measuring heat flow through nanoscale systems poses formidable
practical difficulties as there is no 'ampere meter' for
heat. We propose to overcome this problem by realizing heat
transport through a chain of trapped ions. Laser cooling
the chain edges to different temperatures induces a current
of local vibrations (vibrons). We show how to efficiently
control and measure this current, including fluctuations,
by coupling vibrons to internal ion states. This demonstrates
that ion crystals provide a suitable platform for studying
quantum transport, e.g., through thermal analogues of quantum
wires and quantum dots. Notably, ion crystals may give access
to measurements of the elusive large fluctuations of bosonic
currents and the onset of Fourier's law. Our results are
supported by numerical simulations for a realistic implementation
with specific ions and system parameters.
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Alessandro Cerè
Center for Quantum Technologies, National University of Singapore,
3
Coauthors: Siddarth Koduru Josh (Center for Quantum Technologies,
Singapore), Chen Ming Chia
(Center for Quantum Technologies, Singapore), JeanDaniel
Bancal (Center for Quantum
Technologies, Singapore), Sae Woo Nam (National Institute
of standards and Technology,
Boulder CO), Valerio Scarani (Center for Quantum Technologies
and National
University of Singapore), Christian Kurtsiefer (Center for
Quantum Technologies and
National University of Singapore)
Toward The Generation Of Bell Certified Randomness
Using Photons
Randomness plays a fundamental part in the security of cryptographic
protocols and in the accuracy of numerical simulations.
A system that violates a Bell inequality can be used to
generate random numbers that are certified, i.e. both secure
and truly random [1]. We present our progresses toward an
experimental demonstration of a violation of the CHSH inequality
closing the detection loophole for nearinfrared photons.
This setup will be used for the generation of certified
randomness. We developed an algorithm that takes into account
the full statistics of measured correlations to quantify
the amount of usable private randomness generated. This
provides a tighter bound than the one provided using only
the observed value of the CHSH operator.
The source is based on a periodically poled KTP crystal,
pumped by UV light in two opposite directions, inserted
in a Sagnaclike configuration [2]. It generates photon
pairs at 810nm with an adjustable degree of entanglement
in polarisation. We use two high detection efficiency (
> 95 %) transition edge sensors (TES) [3]. Including
all losses we measure an overall pair detection efficiency
larger than 70 %, which is sufficient to close the detection
loophole. We demonstrate that choosing the appropriate time
binning for the detection of events, only two detectors
are necessary to measure the same violation that could be
measured by using four detectors of the same efficiency.
The setup presented can be extended to close the remaining
loopholes to obtain a complete loophole free violation of
the CHSH Bell inequality.
[1] S. Pironio et al., Nature 464, 1021 (2010).
[2] M. Fiorentino et al., Phys. Rev. A 69, 041801 (2004).
[3] A. E. Lita et al., Opt. Express 16, 3032 (2008).
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M. Cramer Ulm University
Coauthors
O. Marty, A. Bernard, N. Fabbri, L. Fallani, C. Fort, S. Rosi,
F. Caruso, M. Inguscio, and
M.B. Plenio
Quantifying entanglement with simple measurements
Some recent results concerning ways to quantify entanglement
in manybody systems will be reported. At the hand of experimentally
available systems, I will demonstrate how already available
measurements can suffice to quantify the amount of entanglement:
Given a set of observables, we consider all density matrices
that are compatible with measured expectation values of
these observables. Amongst these density matrices, we find
the one with the least amount of entanglement as quantified
by a suitable entanglement measure. In this way, we determine
a lower bound on the entanglement that must have been present
in the state that gave rise to the observed expectation
values. Examples will include recently realized spinsystem
quantum simulators and Neutron scattering from magnetic
materials. Finally, I will present results on the first
experimental quantification of entanglement in bosons in
optical lattices.
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Keiichi Edamatsu Research Institute
of Electrical Communication, Tohoku University
Coauthors: SoYoung Baek, Fumihiro Kaneda, Masanao Ozawa
Experimental test of errordisturbance uncertainty
relations in generalized photonpolarization
measurements
We report an experimental test of errordisturbance uncertainty
relations exploiting a generalized measurement for a singlephoton
polarization quit. The test is carried out by linear optical
devices that realize variable measurement strength from
a weak measurement to a projection measurement. Two exploited
methods, the threestate method and the weak
measurement method, consistently show that Heisenberg's
relation is violated throughout the range of our measurement
strength and yet validates Ozawa's relation. A correct understanding
and experimental confirmation of the errordisturbance uncertainty
relation will not only foster an insight into fundamental
limitations of measurements but also advance the precision
measurement technology in quantum information processing.
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Nicolas Gisin University of Geneva
Coauthors
N. Bruno, A. Martin, P. Sekatski, N. Sangouard, R. T. Thew
Displacing entanglement back and forth between the
micro and macro domains
Quantum theory is often presented as the theory describing
the microscopic world, and admittedly, it has done this
extremely well for decades. Nonetheless, the question of
whether it applies at all scales and in particular at human
scales remains open, despite considerable experimental effort.
Here, we report on quantum entanglement involving two macroscopically
distinct states, i.e. two states characterised by a large
enough number of photons to be seen, at least in principle,
with our naked eyes and that could be efficiently distinguished
using "classical detectors", i.e. detectors sensitive
only to the photon numbers and coarsegrained by thermal
noise. Specifically, we start by thegeneration of entanglement
between two spatially separated optical modes at the single
photon level and subsequently displace one of these modes
up to hundreds of photons. To reliably check whether entanglement
is preserved, the state is redisplaced back to the single
photon level and a wellestablished entanglement measure,
based on single photon detection is performed. The reported
micromacro state exhibits strong analogies with the famous
Schroedinger cat where an initial micro entanglement between
an atom and a photon is mapped with a local unitary to the
entanglement between the atom and a cat, and where the dead
and alive components can be distinguished with a limited
detector resolution. Our results thus provide a fascinating
tool to probe fundamental questions about quantum theory
and holds potential for more applied problems such as quantum
sensing.
1. P. Sekatski, N. Sangouard, M. Stobinska, F. Bussieres,
M. Afzelius, and N. Gisin, Phys.
Rev. A 86, 060301(R) (2012).
2. N. Bruno, A. Martin, P. Sekatski, N. Sangouard, R. T.
Thew, and N. Gisin,
arXiv:1212.3710
3. A. I. Lvovsky, R. Ghobadi, C. Simon, A. Chandra, A. S.
Prasad, arXiv:1212.3713
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Michael Hall Centre for Quantum
Dynamics, Griffith University (Brisbane, Australia)
Coauthors
Morgan Weston, Matthew Palsson, Howard Wiseman and Geoff Pryde.
Experimental test of universal complementarity relations
The principle of complementarity, considered by Niels Bohr
to lie at the heart of quantum theory, asserts that the
respective experimental arrangements for accurately measuring
two quantum observables are, in general, physically incompatible.
Thus, it restricts the degree of accuracy with which joint
information about the observables can be extracted, in any
given experimental setup. Neither Heisenbergtype uncertainty
relations, referring to measurements of 'A or B', normeasurementdisturbance
relations [1,2], referring to measurements of 'A then B',
quantify this principle. Instead, "complementarity
relations" must refer to measurements
of 'A and B', and in particular must limit the accuracy
with which A and B can be simultaneously estimated.We report
the experimental verification of universally valid complementarity
relations [3,4], including of a new such relation. Our experiment
exploited EinsteinPodolskyRosen correlations between two
photonic qubits, to jointly measure incompatible observables
of one [5]. The product of the measurement inaccuracies
was low enough to violate the widely used, but not universally
valid, ArthursKelly relation. Moreover, the measurement
inaccuracies were determined via a method relying on semiweak
measurements and contextual values, rather than on state
tomography [1] or weak measurements [2].
[1] J. Erhart et al., Nature Phys. 8 (2012) 185
[2] L. A. Rozema et al., Phys. Rev. Lett. 109} (2012) 100404
[3] M. J. W. Hall, Phys. Rev. A 69 (2004) 052113
[4] M. Ozawa, Phys. Lett. A 320 (2004) 367
[5] M. M. Weston et al., arXiv:1211.0370 [quantph]
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Bas Hensen Kavli Institute of
Nanoscience Delft, Delft University of Technology, P.O.
Box 5046, 2600 GA Delft, The Netherlands
Coauthors
H. Bernien, W. Pfaff, G. Koolstra, M. S. Blok, L. Robledo,
T. H. Taminiau, M. Markham,
D. J. Twitchen, L. Childress, R. Hanson
Heralded entanglement between solidstate qubits
separated by 3 meters
One of the most intriguing phenomena in quantum physics
is the entanglement of spatially separated objects. The
outcomes of independent measurements on entangled objects
show correlations that cannot be explained by classical
physics. In addition to being of fundamental interest, entanglement
is a unique resource for quantum information processing
and communication. Entangled qubits can be used to establish
private information or implement quantum logical gates[1].
Such capabilities are particularly useful when the entangled
qubits are spatially separated[24], opening the opportunity
to create highly connected quantum networks[5]. Here we
present a key experiment towards the realization of scalable
quantum networks with solidstate qubits[6]. We have entangled
the electron spins of two individual nitrogen vacancy (NV)
centers in diamond, separated by a distance of three meters.
We establish this entanglement using a robust protocol based
on a joint measurement on single photons that are entangled
with the electron spins of the two NV centers. The detection
of the photons projects the spins into an entangled state.
We verify the high quality of the generated quantum correlations
by performing singleshot readout[7] on both NV spins individually
in different bases.
The NV electron spin can act as a bus in a quantum register
formed by surrounding nuclear spins[8]. These nuclear spin
registers can provide the required longlived local memory
that enables deterministic teleportation, quantum repeaters
and extended quantum networks. We will present our latest
results towards deterministic teleportation of a nuclear
spin state on one side to the remote electronic spin.
Finally, by increasing the distance between the entangled
qubits, our results open the door to various tests of quantum
nonlocality. We will present our prospects for a loopholefree
Bell test.
[1] R. Raussendorf & H. J. Briegel, Phys. Rev. Lett.
86, 51885191 (2001).
[2] D. L. Moehring et al., Nature, 449, 68 (2007)
[3] S. Ritter et et al., Nature, 484, 195 (2012)
[4] J. Hofmann et al., Science, 337, 72 (2012)
[5] H. J. Kimble, Nature, 453, 1023 (2008)
[6] H. Bernien et al., Nature (in press), arXiv: 1212.6136
(2013)
[7] L. Robledo et al., Nature, 574, 477 (2011)
[8] W. Pfaff et al., Nature Physics 9, 2933 (2013)
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Khabat Heshami Institute for
Quantum Science and Technology, University of Calgary
Coauthors
C. Healey, B. Khanaliloo, V. Acosta, C. Santori, P. Barclay
and C. Simon
Raman optical quantum memory in NV ensembles coupled
to a cavity
Nitrogen vacancy (NV) centers in diamond are attractive
for applications in quantum information processing. We propose
a scheme based on NV ensembles in a microcavity for implementing
an optical quantum memory based on the Raman quantum memory
protocol. The Raman protocol is known to be suitable for
ensembles of atoms with optical inhomogeneous broadening,
e.g. Dopplerbroadened atomic vapors. The optical
excitation is stored in the ground state electronic spin
coherence of the NV ensemble. We consider all possible optical
transitions from the ground state triplet to excited state
triplets under the effect of electric field (strain) and
magnetic field. As a result, we show that efficient optical
quantum memory can be realized in NV ensembles that are
coupled to microcavities. This proposal may lead to micronscale
implementations of optical quantum memories for possible
applications in quantum information processing schemes based
on integrated quantum photonics.
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Holger F. Hofmann Graduate School
of Advanced Sciences of matter, Hiroshima University, Kagamiyama
131, Higashi Hiroshima 7398530, Japan
Weak measurement statistics as fundamental law of physics:
How inequality violations originate from deterministic relations
between the properties of a quantum system
In classical physics, all properties of a system are deterministic
functions of the phase space coordinates (x,p). In quantum
mechanics, a similar relation is obtained in weak measurements,
where the weak value is a function of preparation a>
and measurement b> [1]. Using projection operators,
the relation between a potential measurement outcome m>
and the set of conditions (a,b) can be described by a complex
conditional probability p(ma,b), where the complex phase
describes the action of a transformation between a and b
generated by m [2]. Here, I point out that the expression
of dynamics in terms of complex probabilities requires negative
probabilities in the joint statistics of noncommuting properties
related by halfperiod transformations. Inequality violations
are therefore the necessary consequence of a fundamental
law of physics that defines joint probabilities in terms
of the action of transformations describing the deterministic
relations between the noncommuting properties of a quantum
system.
References:
[1] Complex joint probabilities as expressions of reversible
transformations in quantum mechanics
H. F. Hofmann, New J. Phys. 14, 043031 (2012)
[2] On the role of complex phases in the quantum statistics
of weak measurements
H. F. Hofmann, New J. Phys. 13, 103009 (2011)
Gregory A. Howland University
of Rochester Department of Physics and Astronomy
Coauthors
John C. Howell (University of Rochester)
Imaging Spatial Entanglement with Compressive Sensing
Biphotons produced in parametric downconversion provide
very high dimensional entanglement in the transverse position
and transverse momentum degrees of freedom. This entanglement
has traditionally been probed by raster scanning singlepixel,
photoncounting detectors through appropriate detection planes.
This approach quickly becomes untenable with increasing
spatial resolution because the requisite number of measurements
increases while the available flux per measurement decreases.
To overcome these limitations, we turn to the to burgeoning
field of Compressive Sensing, a method of compressing a
signal during measurement. This provides a dramatic reduction
in the number of measurements, while individual measurements
use available light more efficiently.
We implement a doublepixel compressivesensing camera to
characterize transverse spatial photonic entanglement. Our
technique leverages sparsity in spatial correlations between
entangled photons to improve acquisition times over raster
scanning by a scaling factor up to n^2/log(n) for ndimensional
images. This can reduce measurement time from a year to
only a few hours. We image at resolutions up to 1024 dimensions
per detector and demonstrate a channel capacity of 8.4 bits
per photon. By comparing the entangled photons' classical
mutual information in conjugate bases, we violate an entropic
EinsteinPodolskyRosen separability criterion.
References:
1) G. A. Howland and J. C. Howell, Efficient HighDimensional
Entanglement Imaging
with a CompressiveSensing DoublePixel Camera, Phys. Rev.
X 3, 011013 (2013)
2) E. J. Candes and M. B. Wakin, An Introduction to Compressive
Sampling, IEEE
Signal Process. Mag. 25, 21 (2008). `
3) J. Schneeloch, P. B. Dixon, G. A. Howland, C. J. Broadbent,
and J. C. Howell,
Violation of ContinuousVariable EinsteinPodolskyRosen
Steering with Discrete
Measurements Phys. Rev. Lett. 110, 130407 (2013).
4) P. B. Dixon, G. A. Howland, J. Schneeloch, and J. C.
Howell, Quantum Mutual
Information Capacity for HighDimensional Entangled States,
Phys. Rev. Lett. 108,
143603 (2012).
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Chengyong Hu Department of E & E,
University of Bristol, United Kingdom
Coauthors: J.G. Rarity
Solidstate quantum communications
and quantum computation based on single
quantumdot spin in optical microcavities
A fascinating dream in quantum information science is to
build quantum computers with superperformance and quantum
networks with unconditional security [1]. Quantum networks
utilize static (matter) quantum bits (qubits) to store and
process quantum information at local nodes, and photons
as flying qubits for longdistance quantum state transmission
between different nodes. To realize a quantum network, it
is crucial to achieve lightmatter entanglement and reversible
quantumstate transfer between light and matter, i.e., the
lightmatter quantum interface, and the quantum repeater
for largescale quantum communications [2].
Recent experiments have shown that both electrons and holes
confined in semiconductor quantum dots (QDs) have long spin
relaxation time (T1e, T1h ms) and long spin coherence time
(T2e ?s, T2h > 100 ns). Moreover, fast spin cooling and
ultrafast spin manipulation as well as spin echoes to preserve
the spin coherence have also been demonstrated. Undoubtedly
these rapid progresses imply that the QD spin is a good
candidate for matter qubit in quantum information processing.
Furthermore, QDbased single photon sources have been also
developed. Therefore, semiconductor QDs offer a good platform
for solidstate quantum networking and quantum computation.
Here we present two types of conditional quantum gates,
i.e., the photonspin entangling gates [34] using a single
QD spin in a singlesided or doublesided optical microcavity.
Both gates are universal and deterministic (if they are
optimized). The spinselective coherent photonspin interaction
enhanced by the cavity QED lead to giant circular birefringence,
which allows us to build these gates. We will show the versatile
spincavity systems can be applied in all aspects of quantum
information science and technology, not only for largescale
quantum communication networks (solidstate quantum repeaters)
[5], but also for scalable quantum computing with either
photons or spins as qubits. We will also discuss other applications
using these gates, such as photonnumber resolving detection,
quantum feedback control, lossresistant quantum
metrology, and loopholefree Bell test [6], and other devices
based on optical nonlinearity at singlephoton levels in
these gate structures. All these schemes are feasible with
current semiconductor technology [7], and we have recently
seen conditional phase shifts in uncharged QDcavity systems
[8].
References
[1] H.J. Kimble, Nature (London) 453, 1023 (2008). [2] H.J.
Briegel et al., Phys. Rev.
Lett. 81, 5932 (1998). [3] C.Y. Hu et al., Phys. Rev. B
78, 085307 (2008); ibid. 78,
125318 (2008). [4] C.Y. Hu et al., Phys. Rev. B 80, 205326
(2009). [5] C.Y. Hu and J.G.
Rarity, Phys. Rev. B 83, 115303 (2011). [6] N. Brunner et
al., Arxiv: quantphys
1303.6522 (2013). [7] S. Reitzenstein et al., Appl. Phys.
Lett. 90, 251109 (2007). [8] A.B.
Young et al., Phys. Rev. A 84, 011803 (2011).
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Gustavo Lima Center for Optics
and Photonics, MSINucleus for Advanced Optics,
Departamento de Física, Universidad de Concepción,
Chile.
Coauthors
A. Cuevas, G. Carvacho, G. Saavedra, J. Cariñe, M.
Figueroa, A. Cabello, P. Mataloni, G.
Lima and G. B. Xavier.
Long distance propagation of genuine energytime
entanglement.
We have recently reported on an experimental violation of
the BellClauserHorne ShimonyHolt (BellCHSH) inequality
using energytimeentangled photons [Phys. Rev. A 81, 040101(R)
(2010)]. The experiment was not free of the locality and
detection loopholes but was the first violation of the BellCHSH
inequality free of the postselection loophole described
by Aerts et al. [Phys. Rev. Lett. 83, 2872 (1999)]. This
loophole affects all previous BellCHSH experiments with
energytime or timebinentangled photons. Our scheme is
based on a modification of the of Franson's scheme, where
the rejection of events is now local. Here we demonstrate
that such scheme can be used for the long distance propagation
of genuine energytime entanglement. This is done by propagating
energytime entangled
photons through optical fiber based interferometers, which
arms are larger than 1,140 km. The twophoton interference
curves observed have a mean raw visibility equal to 0.85
and the corresponding BellCHSH inequality violation is
S = 2.4. The work presented here is an important step towards
the simultaneous closure of the locality and postselection
loopholes in a single experiment with energytime entangled
photons.
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Jeff Lundeen Physics Dept.,
University of Ottawa
Coauthors
Charles Bamber, Measurement Science and Standards, National
Research Council, Ottawa, Canada
Experimental measurement of a point in phasespace:
Observing Dirac's classical analog to the quantum state
There is no universal method to translate the mathematical
description of a classical measurement to its quantum counterpart.
Consider measuring whether a system is at a point in positionmomentum
phasespace. The quantum version of this measurement might
be sought by beginning with the classical description of
this phasespace point, a twodimensional Dirac delta function
centered at x and p, d(Xx, Pp).But the quantum analog
of this depends on one's choice of operator ordering O when
substituting operators Q and K for classical variables X
and P: ?_O(x,p)={d(Qx, Kp)}_O.
Each ordering corresponds to a distinct point operator ?_O,
which may or may not describe a physical measurement. The
antinormal and symmetric orderings correspond to measurements
that directly output the Qfunction and Wigner function
at point (x,p) of the measured quantum state ? [1]. In his
little known attempt to "develop a formal probability"
for a quantum operator [2], Dirac instead considered the
standard ordering S. We experimentally show that we can
directly measure Dirac's probability Pr(x,p) = ?_S(x,p),
and that it has a simple interpretation in terms of a joint
measurement of position and then momentum on the same system
[4]. We then use Dirac's probability distribution to completely
determine and represent a mixed quantum state ?.
We measure the Dirac distribution of the quantum state corresponding
to the transverse positionmomentum of a photon. Photons
exit an optical fiber with identical transverse states.
We introduce phasenoise by rotating a glass plate intersecting
one half of the transverse state, producing a mixed state.
We perform a weak measurement of position Q (by inducing
a small polarization rotation at x) followed by strong measurement
of momentum K with a camera. The result is equal to Dirac's
probability. However, since it contains both a real and
imaginary component it is not a true probability but a quasiprobability,
much like the Wigner function. The two components respectively
correspond to the average polarization rotation in the linear
and circular basis at the camera plane. We show that a 1d
Fourier transform of Dirac's Distribution Pr(x,p) along
the momentum axis gives the density matrix ? of the state.
The Dirac Distribution state representation has three unique
features: 1. Its measurement is simple and similar to the
classical equivalent in phase space. 2. It is compatible
with Bayes' theorem, with which we can propagate it to other
points in space or time. 3. In the limit of a pure quantum
state, it reduces to quantum wavefunction itself, as measured
in Ref [3].
[1] K. Banaszek and K. Wodkiewicz, Phys. Rev. Lett. 76,
4344 (1996), U. Leonhardt, Measuring the quantum state of
light, (Cambridge U. Press, 1997), J. F. Kanem, S. Maneshi,
S. H. Myrskog, and A. M. Steinberg, J. Opt. B 7, S705 (2005).
[2] P. A. M. Dirac, Rev. Mod. Phys. 17, 195 (1945).
[3] J. S. Lundeen, B. Sutherland, A. Patel, C. Stewart,
and C. Bamber, Nature 474, 188 (2011).
[4] J. S. Lundeen and C. Bamber, Phys. Rev. Lett. 108, 070402
(2012).
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Roee Ozeri Weizmann Institute of
Science
Coauthors
Shlomi Kotler, Nitzan Akerman, Yinnon Glickman, Nir Navon
Active Decoherence Suppression methods in Metrology
Decoherence limits to the accuracy of quantum sensors. In
quantum computing, methods were developed to suppress decoherence.
Dynamic decoupling, the encoding of information in decoherencefreesubspaces,
and quantum errorcorrection, have all been implemented
in quantum computing experiments and enabled the prolongation
of coherence times. Here I will describe how we use active
decoherence suppression in trapped ion qubits in order to
improve the accuracy of precision measurements. We have
shown how dynamic modulation techniques, analogues to the
lockin amplifier methods can be used to improve the sensitivity
of phase evolution under Zeeman and Stark shifts [1,2].
We used a decoherence free subspace to measure magnetic
field gradients and the magnetic interaction between two
electronic spins of ions that were separated by more than
2 microns. Lastly I will discuss the prospects of using
quantum errorcorrection techniques to improve on precision
measurements.
[1] S. Kotler, N. Akerman, Y. Glickman, A. Keselman, and
Roee Ozeri, "Single Ion
Quantum LockIn Amplifier" Nature 473, 61 (2011)
[2] S. Kotler, N. Akerman, Y. Glickman and R. Ozeri, "Nonlinear
single spin spectrum
analyzer", Phys. Rev. Lett. 110, 110503, (2013)
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Marco Piani Institute for Quantum
Computing, University of Waterloo
Coauthors
Patrick J. Coles (Centre for Quantum Technologies, National
University of Singapore, 2
Science Drive 3, 117543 Singapore)
Entanglementbased uncertainty principle for sequential
measurements
We offer a novel view on what complementarity of observables
entails. We consider sequential measurements performed on
the same physical system and we focus on the entanglement
generated between the system and the measurement devices
that interact with the system in sequence. In the case where
the two observables are complementary, sequentially measuring
them produces maximal entanglement, for all possible initial
states of the system. This is not true for noncomplementary
observables. However, in general, for any pair of observables
we can lowerbound the entanglement between the system and
the measurement devices created from the sequential measurement,
independently of the input state of the system. Such lower
bound has a striking resemblance to wellknown entropic
relations lowerbounding the uncertainty in the
measurement of the two observableseach independently
measured on independent but identically prepared copied
of the same physical system. Our approach relates in a novel
way two basic concepts of quantum mechanics: complementarityin
the sequentialmeasurement scenarioand entanglement. Besides
this fundamental interest, our results have direct operational
interpretations. On one hand, they provide bounds on the
usefulness of sequential bipartite operationscorresponding
to the measurement interactionsfor entanglement generation.
On the other hand, we prove that our approach is directly
linked to the quantum information processing primitives
of decoupling and coherent teleportation: the bound on entanglement
creation is also abound on the level of accuracy for the
said tasks, as realized by means of the coherent measurement
of the two observables.
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Sadegh Raeisi Institute for Quantum
Computing
Coauthors
Robabeh Rahimi Darabad, Jonathan Baugh, Raymond Laflamme
High Polarization of Nuclear Spins by Modulating
a Coupled Electron Spin
Spin systems are known to be among the most promising candidates
for exploiting quantum effects, yet one of the key challenges
to harness this quantum power, is to overcome thermal fluctuations
and prepare a pure quantum state for spins. Highly pure
or "polarized" spins are a key requirement in
many applications like high resolution imaging using spin
resonance in MRI and fault tolerant quantum computation.
Here we use a method called "HeatBath Algorithmic
Cooling" to prepare highly polarized spins. This method
has been previously used to polarize one spin to twice as
much as its equilibrium polarization. Here we increase this
factor about 10^{3} times using an electron spin. Specifically
we use the free radical of Gamma irradiated Malonic acid
to polarize and control the nuclear spins. In other words,
the electron spin is used both as the polarization bath
and for the control of two nuclear spins. In order to control
the nuclear spins through the manipulation of the electron
spin, we exploit the hyperfine interaction that couples
nuclei to electron. This method could have potential applications
in high resolution MRI imaging and spinbased quantum information
science.
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Paul RaymondRobichaud
Université de Montréal
Coauthors
Gilles Brassard
Parallel Lives
We show how to make perfect nonlocal (PopescuRohrlich)
boxes in a local realistic toy model. Our toy model has
various similarities to ideas from Everett's "relative
state" formulation of quantum mechanics (1957), but
does not inherit any of the hard conceptual problems of
the manyworld view, such as the preferred basis or the
emergence of probabilities. This work has the following
philosophical consequence: A Bell inequality can be maximally
violated (even more so than allowed by quantum mechanics)
in an extremely simple, yet purely local realistic world.
We examine the 1935 EinsteinPodolskyRosen argument and
Bell's theorem in the light of this toy model. Bell's theorem
should be seen as a proof that local hidden variable theories
are not compatible with a violation of Bell's inequality,
as correctly stated by Bell himself, but this is only one
possible class of local realistic theories. Other such theories
can exist on which Bell's theorem has no impact.
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Jacquiline Romero University
of Glasgow
Coauthors
Daniele Giovannini, Daniel Tasca, Miles J. Padgett
A nontrivial trivial detection loophole
We demonstrate an experimental test of the ClauserHorneShimonyHolt
(CHSH) inequality exploiting a nontrivial detection loophole.
This loophole, which allows us to observe correlation beyond
the limits imposed by quantum mechanics, persists even when
using perfectly efficient single photon detectors [1, 2].
Tests of the CHSH inequality are designed as twoparty,
twosetting, twooutcome experiments, where it is assumed
that all measurements are made within the same statespace
[3]. In our experiment, a subtle choice of measurement states
leads to analysers which, upon physical rotation, sample
different, intersecting subsets of the total Hilbert space.
Together with postselection, this choice of analysers seemingly
allows for superquantum violations of the CHSHBell inequality
with the Bell parameter, S, taking values beyond the Tsirelson
bound of S=2v2. We obtain a maximum value of, S=3.99, implying
almost perfect nonlocal PopescuRohrlich correlations [2].
Our experiment highlights the caution needed in Belltype
experiments based on measurements within highdimensional
state spaces, where postselection arises not just in the
inefficiency of the detectors.
1. Cirel'son, B. S. , Quantum generalizations of Bell's
inequality, Lett. Math. Phys. 4, 93
100 (1980). 2. Popescu S. and Rohrlich D., Quantum nonlocality
as an axiom, Found.
Phys. 24, 379385 (1994). 3. Dada A. and Andersson E., On
Bell inequality violations
with highdimensional systems, Int. J. Quantum Inf. 9, 18071823
(2011).
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James Schneeloch University
of Rochester
Coauthors
Curtis J. Broadbent (University of Rochester) Stephen P. Walborn
(Universidade Federal
do Rio de Janeiro) Eric G. Cavalcanti (University of Sydney)
John C. Howell (University
of Rochester)
EinsteinPodolskyRosen Steering Inequalities from
Entropic Uncertainty Relations
In quantum information, entanglement and other forms of
nonlocal correlation (e.g. EinsteinPodolskyRosen (EPR)
steering [1]) can be an essential resource. Given that most
useful findings and criteria in information theory are formulated
in terms of Shannon's entropy, witnesses of nonlocal correlations
expressed in terms of entropies can be very useful. We examine
a particular class of nonlocal correlations known as EPR
steering, a level of nonlocal correlation between a pair
of systems sufficient to demonstrate the EPR paradox [2],
but not to rule out models of local hidden variables.
First, we show by demonstration that EPRsteering inequalities,
whose violation rules out a local state description for
one system, can be created whenever observable quantities
are connected by an entropic uncertainty relation. We develop
steering inequalities between any pair of observables, between
discrete positive operator value measures (POVMs), and between
complete sets of mutually unbiased observables. In addition,
we develop hybrid EPRsteering inequalities, whose violation
witnesses EPRsteering correlations (and entanglement) across
disparate degrees of freedom. Next, we develop symmetric
EPRsteering inequalities using the mutual information,
whose violation rules out a local state description for
both systems in the pair at the same time. In quantum key
distribution, we show that demonstrating symmetric EPR steering
is sufficient to prove that the channel is secure against
interceptresend attacks, even when Alice and Bob don't
trust each other, but trust their own devices. Finally,
we examine the possible existence of exclusively oneway
steerable states using Monte Carlo simulations of random
twoqubit states.
References:
[1] H. M. Wiseman, S. J. Jones, and A. C. Doherty, Phys.
Rev. Lett. 98, 140402 (2007).
[2] A. Einstein, B. Podolsky, and N. Rosen, Phys. Rev. 47,
777 (1935).
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Olga Sminrova MaxBorn Institute
Coauthors
J. Kaushal, L. Torlina, M. Ivanov
Attosecond Larmor clock
We have introduced a rigorous definition of the time it
takes to remove an electron and create a hole, derived from
the first principles of quantum mechanics. It is applicable
to any photoionization process, from onephoton to multiphoton
to lightinduced tunnelling. The definition is based on
a physical clock naturally built into many atoms and molecules.
It operates on spinorbit interaction, mapping precession
of the electron or hole spin on time. The spinorbit dynamics
is not affected by the laser field, making the clock robust.
Using this clock, we find two types of delays: real delays
in the formation of a hole, and apparent delays associated
with electronhole entanglement. The latter results in modifying
the hole wavepacket, stretching or compressing it during
the electron removal.
Using the example of a Kr atom, we analyse delays vs the
number of absorbed photons and show that absorption of many
lowenergy photons may create holes faster than absorption
of one photon of the same total energy. Strongfield ionization
is often viewed as electron tunnelling through the barrier
created by the laser field and the core potential. Our new
definition also allows us to revisit the
question about tunnelling delays. We predict that if recorded,
tunnelling delays signify the presence of nonequilibrium
charge dynamics excited inside an atom or a molecule. We
show direct link between the ionization time defined in
our work and the ionization delay measurements attempted
in two opposite regimes: onephoton ionization and optical
tunnelling.
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T. H. Taminiau Delft University
of Technology
Coauthors
T. H. Taminiau1, W. Pfaff1, T. van der Sar1, J. Cramer1, H.
Bernien1, M. S. Blok1, J. J.
T. Wagenaar1, M. L. Markham2, D. J. Twitchen2, L. Robledo1,
V. V. Dobrovitski3, R.
Hanson1
Measurementbased entanglement and Bell inequality
violation with individual solidstate
spins
The nitrogen vacancy (NV) center in diamond is one of the
most promising candidatesfor solidstate quantum information
processing. The optically active NV electronic spin is readily
manipulated and can be used to access individual nuclear
spins in the environment so that a robust quantum register
is formed. Here I will present a key step to realize the
full potential of such diamond quantum registers: the creation
of an entangled state of two nuclear spins. We implemented
a nondestructive parity measurement that projects two nuclear
spins near an NV center into highly entangled states and
demonstrated the first violation of a Bell inequality with
solidstate spins [1]. Because we do not assume fair sampling,
this result proves the formation of a pure entangled state
of nuclear spins. Finally, I will discuss our recent progress
on implementing 3qubit quantum error correction codes by
combining these results with our recent demonstration of
decoherenceprotected gates [2] that extend the number of
nuclear spins that can be controlled [3]. Together these
results establish a new class of experiments in which
projective measurements create, protect and manipulate large
entangled states of solidstate qubits.
[1] W. Pfaff et al., Nature Phys. 9, 29 (2013)
[2] T. van der Sar et al., Nature 484, 82 (2012)
[3] T. H. Taminiau et al., Phys. Rev. Lett. 109, 137602
(2012)
T. H. Taminiau1, W. Pfaff1, T. van der Sar1, J. Cramer1,
H. Bernien1, M. S. Blok1, J. J.
T. Wagenaar1,
M. L. Markham2, D. J. Twitchen2, L. Robledo1, V. V. Dobrovitski3,
R. Hanson1
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Harald Weinfurter, Faculty
of Physics, LudwigMaximiliansUniversity, MaxPlanck
Institut for Quantum Optics, Garching, Germany
Coauthors
Daniel Burchardt, Julian Hofmann, Michael Krug, Norbert Ortegel,
Kai Redeker, Markus Weber, Wenjamin Rosenfeld, and Harald
Weinfurter
Heralded entanglement between widely separated atoms
A route towards a loophole free test of Bell's inequality
?
Entanglement is the essential feature of quantum mechanics.
Its importance arises from the fact that observers of two
or more entangled particles will nd correlations in their
measurement results, which can not be explained by classical
statistics. Heralding the entanglement between distant quantum
systems makes it an even more useful resource for, e.g.,
scalable longdistance quantum communication or for loophole
free tests of Bell's inequality. Here we report on the generation
and analysis of heralded entanglement between spins of two
single Rb87 atoms trapped independently 20 meters apart
and how to use this to teleport the polarisation state of
light onto the distant atom. The data observed violate a
Bell type entanglement without the detection loophole even
for the large separation. We discuss the progress towards
further extending this experiment to also close the locality
loophole. For that purpose the measurements, now taking
about 20 ms only for the readout, have to be performed signi
cantly faster. We are developing a fast quantum random number
generator determining the analysis direction and are currently
implementing state dependent ionization and subsequent detection
of the ionization fragments allowing to perform the whole
measurement sequence within a microsecond. Together with
extending the distance between the trapped
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Gerardo Viza, University of Rochester
Coauthors: Julian MartnezRincon, Gregory A. Howland, Hadas
Frostig, Itay Shomroni, Barak Dayan,and John C. Howell
Weakvalues technique for Velocity Measurements
In a recent letter, Brunner and Simon propose an interferometric
scheme using imaginary weak values with a frequencydomain
analysis to outperform standard interferometry in longitudinal
phase shifts [N. Brunner and C. Simon, Phys. Rev. Lett 105
(2010)]. Here we demonstrate an interferometric scheme combined
with a timedomain analysis to measure Doppler shifts. The
technique employs looking at the neardestructive interference
of temporally incoherent pulses, one Doppler shifted due
to a moving mirror, in a Michelson interferometer. We achieve
a measurement of Doppler shift down to the microHz range
and show our estimator to be efficient by reaching the CramerRao
bound.
