Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V39: Quantum Foundations IIFocus

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Sponsoring Units: DQI Chair: Ian Durham, St Anselm Coll Room: LACC 501B 
Thursday, March 8, 2018 2:30PM  3:06PM 
V39.00001: EinsteinPodolskyRosen Steering in Quantum Theory and Beyond Invited Speaker: Ana Sainz The discovery of postquantum nonlocality, i.e. the existence of nonlocal correlations stronger than any quantum correlations but nevertheless consistent with the nosignaling principle, has deepened our understanding of the foundations quantum theory. In this talk I discuss how the phenomenon of EinsteinPodolskyRosen steering, a different form of quantum nonlocality, can also be conceived beyond quantum theory. I will present analytical examples of quantum and postquantum steering, and different frameworks to understand them. 
Thursday, March 8, 2018 3:06PM  3:18PM 
V39.00002: Unbounded violation of quantum steering inequality Adam Rutkowski Quantum steering is a relatively simple test for proving that the values of quantummechanical measurement outcomes come into being only in the act of measurement. By exploiting quantum correlations, Alice can influence ( steer ) Bob’s physical system in a way that is impossible in classical mechanics, as shown by the violation of steering inequalities. Demonstrating this and similar quantum effects for systems of increasing size, approaching even the classical limit, is a longstanding challenging problem. Here, we prove an experimentally feasible unbounded violation of a steering inequality. We derive its universal form where tolerance for measurementsetting errors is explicitly built in by means of the Deutsch–Maassen–Uffink entropic uncertainty relation. The method is general and opens the possibility of employing bipartite steering for randomness certification and development of quantum technologies, e.g., random access codes. 
Thursday, March 8, 2018 3:18PM  3:30PM 
V39.00003: Contextuality as a Noiserobust Witness of Nonclassicality: Beyond the CabelloSeveriniWinter Framework Ravi Kunjwal, Robert Spekkens We propose an approach to obtaining noiserobust noncontextuality inequalities within the framework of generalized noncontextuality, inspired by statistical proofs of the KochenSpecker (KS) theorem. This approach works for any such proof of the KS theorem and violation of the resultant noncontextuality inequalities can witness contextuality even if the measurements or preparations in the experiment are noisy or unsharp. Indeed, this approach allows us to generalize the graphtheoretic CabelloSeveriniWinter (CSW) framework to a noiserobust hypergraphtheoretic framework. For the case of quantum theory, we can deal with nonprojective (or unsharp) measurements and resolve the pathologies they lead to in traditional approaches such as CSW. Our noncontextuality inequalities are thus robust to the presence of noise in the experimental procedures, whether they are measurements or preparations, and are applicable to operational theories that need not be quantum. 
Thursday, March 8, 2018 3:30PM  3:42PM 
V39.00004: Bounds on Partial Preparation Noncontextuality Eric Freda, Matthew Leifer We can examine the extent to which preparation contextuality is required to reproduce the predictions of quantum mechanics by considering models that are a convex mixture of a noncontextual model and a contextual model. The maximum weight that can be given to the noncontextual portion of such a model can be used to quantify the preparation contextuality required to explain quantum experiments. In this talk I will discuss bounds on this quantity from 2bit parityoblivious multiplexing and an extension to arbitrary angles. From this argument we can bound the overlap of two representations of the maximally mixed state. 
Thursday, March 8, 2018 3:42PM  3:54PM 
V39.00005: Measurement Contextuality and Planck's Constant Lucas Kocia, Peter Love Contextuality is a necessary resource for universal quantum computation and noncontextual quantum mechanics can be simulated efficiently by classical computers in many cases. Orders of Planck's constant, hbar, can also be used to characterize this classicalquantum divide by expanding quantities of interest in powers of hbarall orders higher than hbar^{0} can be interpreted as quantum corrections to the order hbar^{0} term. We show that contextual measurements in finitedimensional systems have formulations within the WignerWeylMoyal (WWM) formalism that require higher than order hbar^{0} terms to be included in order to violate the classical bounds on their expectation values. As a result, we show that contextuality as a resource is equivalent to orders of hbar as a resource within the WWM formalism and this explains why qubits can only exhibit exhibit stateindependent contextuality under Pauli observables while odddimensional qudits can also exhibit statedependent contextuality. In particular, we find that qubit Pauli observables lack an order hbar^{0} contribution in their Weyl symbol and so exhibit contextuality regardless of the state being measured. 
Thursday, March 8, 2018 3:54PM  4:06PM 
V39.00006: Information indistinguishability and nonlocality Cassio Amorim A physical explanation for quantum bounds to nonlocality (Tsirelson’s bound) is a fundamental problem that remains open, and one approach to explaining its origins is the socalled Exclusivity principle, relying on probabilistic assumptions shaping general probabilistic theories through sharp measurements and compatible (nonlocal) measurements. Information indistinguishability, presented here as indistinguishability of qubits and more general bits, may serve as an answer to the nonlocality conundrum, ultimately placing it as the origin to quantum limits. We connect indistinguishability to the exclusivity principle and show that indistinguishability leads to quantum bounds. With that, we suggest indistinguishability to be as fundamental as nonlocality and relativistic causality for nonlocal realism. 
Thursday, March 8, 2018 4:06PM  4:18PM 
V39.00007: Algebraic ProbabilityTheoretic Characterization of Quantum Correlations Bin Yan A framework of linear hidden variable representation based on the classical algebraic probability theory is introduced. Three major problems are discussed within this framework: 1) the relation between entanglement and nonlocality, 2) the algebraic characterization of nulldiscord states, and 3) quasiprobability representation of quantum states in multipartite systems. 
Thursday, March 8, 2018 4:18PM  4:30PM 
V39.00008: Local HiddenVariable Model for a Recent Experimental Test of Quantum Nonlocality and Local Contextuality Brian La Cour An experiment has recently been performed to demonstrate quantum nonlocality by establishing contextuality in one of a pair of photons encoding four qubits; however, low detection efficiencies and use of the fairsampling hypothesis leave these results open to possible criticism due to the detection loophole. In this talk, a physically motivated local hiddenvariable model is described as a possible mechanism for explaining the experimentally observed results. The model, though not intrinsically contextual, acquires this quality upon postselection of coincident detections. [Physics Letters A 381, 2230 (2017).] 
Thursday, March 8, 2018 4:30PM  4:42PM 
V39.00009: Tests of Macrorealism and Quantum Weak Values for NOON States and BoseEinstein condensates Margaret Reid, Laura RosalesZarate, Bogdan Opanchuk Leggett and Garg suggested testing macroscopic realism by comparing the predictions of quantum mechanics with those based on two premises: macroscopic realism per se and noninvasive measurability: The premises imply an inequality that can be violated for macroscopic quantum superposition states [1]. We construct tests of macrorealism for NOON states [2,3]. These mesoscopic superposition states may be realised optically, or can be created dynamically by a twomode Josephson Hamiltonian that includes the nonlinearity associated with, for example, BoseEinstein condensates. To test the LeggettGarg inequality, one requires a noninvasive measurement. We propose such a measurement for NOON and BEC states [2,3]. The proposed measurement may be realised for atomic systems using an ac Stark shift. For small measurement interaction, we demonstrate weak values, where postselected results exceed the eigenvalue range [4]. We link our results to violation of a Bell inequality. 
Thursday, March 8, 2018 4:42PM  4:54PM 
V39.00010: Null weak values: can the properties of a physical system vanish ? Quentin Duprey, Alex Matzkin The Weak Measurements approach is a framework based on implementing nondestructive, nonperturbing measurements on a quantum system as the system evolves from an initially prepared state to a postselected final state obtained by performing a standard measurement. The result of a weak measurement is called the 
Thursday, March 8, 2018 4:54PM  5:06PM 
V39.00011: Correlators Larger Than One in Continuous Measurement of a Superconducting Qubit Juan Atalaya, Shay HacohenGourgy, Irfan Siddiqi, Alexander Korotkov The interplay of the phase and informational backactions can lead to counter intuitive results. We consider the effect of the phase backaction on the correlator〈I(t) I(t+τ)〉for the output signal I(t) from a continuous measurement of a qubit. We demonstrate that in the presence of Rabi oscillations the correlator can become larger than 1, even though │〈I(t)〉│≤ 1 due to normalization. The bound of 1 for the correlator can be exceeded only when the phase backaction is present. The correlators can be calculated using the generalized "collapse recipe", which we prove using the quantum Bayesian formalism. The recipe can be further generalized to the case of multitime correlators and arbitrary number of phasesensitive detectors, measuring noncommuting qubit observables. The theory agrees well with experimental results for continuous cQED measurement of a transmon qubit. The experimental correlator exceeds the bound of 1 for a sufficiently large angle between the amplified and informational quadratures, causing the phase backaction. The demonstrated effect can be useful for calibration of the quadrature misalignment. 
Thursday, March 8, 2018 5:06PM  5:18PM 
V39.00012: Homodyne monitoring of postselected decay Dian Tan, Neda Foroozani, Mahdi Naghiloo, Alexander Holm Kiilerich, Klaus Molmer, Kater Murch Homodyne measurement of the radiative decay of a quantum emitter can be used to track quantum evolution, yielding stochastic quantum trajectories for the emitter’s state. Here we explore how postselection alters the quantum state dynamics of radiative decay, showing how the probability of finding the emitter in the excited state is modified with postselections at a final time T. We use experimental data based on phase sensitive amplification of the fluorescence from a superconducting qubit to observe anomalous weak values in continuous weak measurement for certain pre and postselected states. We further study the quantum trajectories for certain pre and postslected states and and find that these trajectories are confined to deterministic regions in the Bloch sphere. 
Thursday, March 8, 2018 5:18PM  5:30PM 
V39.00013: The threebox paradox revisited using the Majorana representation of the quantum states Mirko Cormann, Mathilde Remy, Yves Caudano In the quantum threebox paradox, seemingly contradictory conclusions are drawn about the intermediate location of a particle between its initial (preselected) state and its final (postselected) state. We use the Majorana representation of the equivalent 3level quantum system to reformulate the paradox in terms of the symmetric states of a pair of qubits. This provides us with a geometric description of the paradox on the Bloch sphere. In particular, we find that the phase of the weak values associated with the sensing of the particle location in the weak measurement formalism is related to solid angles defining geometric phases. In the Majorana representation of this paradox, the pre and postselected pairs of particles have initial and final states that are separable but their intermediate states are found to be maximally entangled. We describe an experiment which we are currently setting up to investigate this formulation of the paradox using weak measurements of pairs of entangled photons produced by spontaneous parametric downconversion. Reference: M. Cormann and Y. Caudano, J. Phys. A: Math. Theor. 50 (2017) 305302. 
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