Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C52: Quantum Foundations and Entanglement |
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Sponsoring Units: GQI Chair: Shelby Kimmel, University of Maryland Room: 399 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C52.00001: Optimising entanglement distillation Filip Rozpedek, Thomas Schiet, Le P. Thinh, David Elkouss, Andrew C. Doherty, Stephanie Wehner Entanglement distillation is of great importance in many quantum information processing tasks. It allows to convert multiple copies of a noisy entangled state into a smaller number of less noisy entangled states using only local operations and classical communication. Here we investigate the fundamental trade-off between the output fidelity to a maximally entangled state and the probability of success in probabilistic distillation protocols. Due to this trade-off, it has been an open question to find the most efficient protocol. In this work we develop a framework for demonstrating optimality of well-known protocols for specific input states. Using tools of semi-definite programming we obtain upper bounds on the output fidelity for a specific input state and a fixed probability of success. Specifically, we develop a semi-definite programme that optimises the output fidelity over the positive partial transpose operations. We then apply our programme to various states that naturally arise in experimental scenarios. For specific states our bounds are achievable with the DEJMPS (PRL, vol, 77, no. 13 p. 2818, 1996) or the EPL (PRX, vol 4, Iss 12, p. 041041, 2014) protocol, hence demonstrating the optimality of these protocols for those states. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C52.00002: Efficient recurrence quantum entanglement distillation algorithm for quantum channels impaired by fiber birefringence Liangzhong Ruan, Brian T. Kirby, Michael Brodsky, Moe Z. Win Distributing entangled states with high fidelity via fiber optic routes is challenging due to the various decoherence mechanisms in fibers. In particular, one of the primary polarization decoherence mechanism in optical fibers is polarization mode dispersion (PMD), which is the distortion of optical pulses by random birefringences in the system. Among quantum entanglement distillation (QED) algorithms proposed to mitigate decoherence, the recurrence QED algorithms require the smallest size of quantum circuits, and are most robust against severe decoherence. On the other hand, the yield of recurrence QED algorithms drops exponentially with respect to the rounds of distillation, and hence it is critical to minimize the required rounds of distillation. We present a recurrence QED algorithm, which is capable of achieving maximum fidelity in every round of distillation when each photonic qubit individually traverses a PMD-degraded channel. The attainment of optimal fidelity in every round of distillation implies that our algorithm reaches the fastest possible convergence speed and hence requires the minimum rounds of distillation. Therefore, the proposed algorithm provides an efficient method to distribute entangled states with high fidelity via optic fibers. [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C52.00003: Gain maximization in a probabilistic entanglement protocol Antonio Di Lorenzo, Johnny Hebert Esteves de Queiroz Entanglement is a resource. We can therefore define gain as a monotonic function of entanglement $G(E)$. If a pair with entanglement $E$ is produced with probability $P$, the net gain is $N=PG(E)-(1-P)C$, where $C$ is the cost of a failed attempt. We study a protocol where a pair of quantum systems is produced in a maximally entangled state $\rho_m$ with probability $P_m$, while it is produced in a partially entangled state $\rho_p$ with the complementary probability $1-P_m$. We mix a fraction $w$ of the partially entangled pairs with the maximally entangled ones, i.e. we take the state to be $\rho = (\rho_m+wU_{loc}\rho_pU_{loc}^+)/(1+w)$, where $U_{loc}$ is an appropriate unitary local operation designed to maximize the entanglement of $\rho$. This procedure on one hand reduces the entanglement $E$, and hence the gain, but on the other hand it increases the probability of success to $P=P_m +w(1-P_m)$, therefore the net gain $N$ may increase. There may be hence, a priori, an optimal value for $w$, the fraction of failed attempts that we mix in. We show that, in the hypothesis of a linear gain $G(E)=E$, even assuming a vanishing cost $C\to0$, the net gain $N$ is increasing with $w$, therefore the best strategy is to always mix the partially entangled states. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C52.00004: Entanglement distance between quantum states and its implications for density-matrix-renormalization-group study of degenerate ground-states Seyyed Mohammad Sadegh Vaezi, Abolhassan Vaezi We study the concept of entanglement distance between two quantum states, which quantifies the amount of information shared between their reduced density matrices. We will show that for gapless systems the entanglement distance exhibits power law dependence on the energy separation and subsystem size and find the corresponding exponents. We also demonstrate that the entanglement distance reaches its maximum for degenerate ground states of two-dimensional topological phases. Various implications of entanglement distance for quantum simulations will be discussed. In particular, we will introduce two modified density-matrix-renormalization-group algorithms that are capable of finding all degenerate ground-states. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C52.00005: Multi-hop teleportation of an unknown Two-Particle Entangled State via EPR Pairs Xiaoqin Gao, Zaichen Zhang, Xutao Yu A scheme of quantum multi-hop teleportation with an unknown two-particle entangled state based on EPR pairs is proposed. For one-hop teleportation, sender just makes two Bell-state measurements and informs receiver the measured result by classical wireless channel. Then the teleportation will succeed if receiver performs appropriate Pauli operators, and the success probability can reach 1 without any auxiliary particle. For $k$-hop teleportation, except the destination node, all nodes include source node and $k$-1 intermediate nodes must do two Bell-state measurements and the measurement results are sent to the destination node independently. Then, the destination node performs some Pauli operators based on all received measurement results to recover the initial quantum state. By comparison, our scheme is superior to hop-by-hop teleportation and can reduce hop-by-hop teleportation delay and save resources. The scheme of quantum multi-hop teleportation proposed contributes greatly to long-distance quantum key distribution and can be applied to massive quantum network in the future. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C52.00006: Spacetime Replication of Quantum Information Using $(2,3)$ Quantum Secret Sharing and Teleportation Yadong Wu, Abdullah Khalid, Masoud Davijani, Barry Sanders The aim of this work is to construct a protocol to replicate quantum information in any valid configuration of causal diamonds and assess resources required to physically realize spacetime replication. We present a set of codes to replicate quantum information along with a scheme to realize these codes using continuous-variable quantum optics. We use our proposed experimental realizations to determine upper bounds on the quantum and classical resources required to simulate spacetime replication. For four causal diamonds, our implementation scheme is more efficient than the one proposed previously. Our codes are designed using a decomposition algorithm for complete directed graphs, $(2,3)$ quantum secret sharing, quantum teleportation and entanglement swapping. These results show the simulation of spacetime replication of quantum information is feasible with existing experimental methods. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C52.00007: Distribution of Bell-inequality violation versus multiparty-quantum-correlation measures Kunal Sharma, Tamoghna Das, Aditi Sen (De), Ujjwal Sen Violation of a Bell inequality guarantees the existence of quantum correlations in a shared quantum state. A pure bipartite quantum state, having nonvanishing quantum correlation, always violates a Bell inequality. Such correspondence is absent for multipartite pure quantum states in the case of multipartite correlation function Bell inequalities with two settings at each site. We establish a connection between the monogamy of Bell-inequality violation and multiparty quantum correlations for shared multisite quantum states. We believe that the relation is generic, as it is true for a number of different multisite measures that are defined from radically different perspectives. Precisely, we quantify the multisite-quantum-correlation content in the states by generalized geometric measure, a genuine multisite entanglement measure, as well as three monogamybased multiparty-quantum-correlation measures, viz., 3-tangle, quantum-discord score, and quantum-work-deficit score. We find that generalized Greenberger-Horne-Zeilinger states and another single-parameter family of states, which we refer to as the special Greenberger-Horne-Zeilinger states, have the status of extremal states in such relations. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C52.00008: Generation of fresh and pure random numbers for loophole-free Bell tests Morgan Mitchell, Carlos Abellan, Waldimar Amaya, Daniel Mitrani, Valerio Pruneri We describe the physical randomness generation strategy used in the loophole-free Bell tests of 2015 [Hensen et al., Nature (London) 526, 682 (2015); Giustina et al., Phys. Rev. Lett. 115, 250401 (2015); Shalm et al., Phys. Rev. Lett. 115, 250402 (2015)]. A system consisting of telecommunications lasers, detectors, interferometry, and fast analog and digital electronics produces analog signals with a large contribution traceable to spontaneous emission events, and bounded contribution from all other sources. Fast parity-bit randomness extraction is used to produce output bits with excess predictability below $10^{−5}$ due to spontaneous-emission events less than 36 ns in the past. This randomness generation strategy satisfies for the first time the stringent requirements identified in modern statistical analyses of loophole-free Bell tests. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C52.00009: Mermin inequalities for GHZ contradictions in many-qutrit systems Walter Lawrence In view of recent experimental interest [1] in multi-qutrit entanglement properties, we provide here new Mermin inequalities for use in experimental tests of many-qutrit GHZ contradictions, first predicted only recently (2013). Mermin inequalities refer here to Bell-like inequalities in which the quantum predictions are not probabilistic, thus elevating hidden variables to the status of EPR elements of reality. Earlier Bell inequalities for qutrits [2] predate the discovery of GHZ contradictions, are based on non-concurrent observable sets, and hence cannot establish GHZ contradictions. The current Mermin inequalities are derived from those concurrent observable sets which produce GHZ contradictions, with the following results: (i) There is an operator $M$ defined for every $N \geq 4$, built on two measurement bases, whose quantum eigenvalue grows as $2^N$, maximum classical value more slowly ($1.879^N$), with quantum to classical ratio being never less than 1.39, and (ii) For $N=3$, there is an $M_3$, built on three local measurement bases, whose quantum to classical ratio is 3/2. [1] M. Malik et. al., {\it Nature Photonics}, {\bf 10}, 248 (2016), [2] W. Son et. al., {\it Phys Rev. Letters}, {\bf 96}, 060406 (2006). [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C52.00010: Conditional Mutual Information of Bipartite Unitaries and Scrambling Dawei Ding, Patrick Hayden, Michael Walter One way to diagnose chaos in bipartite unitary channels is via the tripartite information of the corresponding Choi state, which for certain choices of the subsystems reduces to the negative conditional mutual information (CMI). We study this quantity from a quantum information-theoretic perspective to clarify its role in diagnosing scrambling. When the CMI is zero, we find that the channel has a special normal form consisting of local channels between individual inputs and outputs. However, we find that arbitrarily low CMI does not imply arbitrary proximity to a channel of this form, although it does imply a type of approximate recoverability of one of the inputs. When the CMI is maximal, we find that the residual channel from an individual input to an individual output is completely depolarizing when the other input is maximally mixed. However, we again find that this result is not robust. We also extend some of these results to the multipartite case and to the case of Haar-random pure input states. Finally, we look at the relationship between tripartite information and its Renyi-2 version which is directly related to out-of-time-order correlation functions. In particular, we demonstrate an arbitrarily large gap between the two quantities. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C52.00011: Deconstruction and conditional erasure of quantum correlations Mario Berta, Fernando Brandao, Christian Majenz, Mark Wilde We define the deconstruction cost of a tripartite quantum state on systems $ABE$ as the minimum rate of noise needed to apply to the $AE$ systems, such that there is negligible disturbance to the marginal state on the $BE$ systems and the system $A$ of the resulting state is locally recoverable from the $E$ system alone. We refer to such actions as deconstruction operations and protocols implementing them as state deconstruction protocols. State deconstruction generalizes Landauer erasure of a single-party state as well the erasure of correlations of a two-party state. We find that the deconstruction cost of a tripartite quantum state on systems $ABE$ is equal to its conditional quantum mutual information (CQMI) $I(A;B|E)$, thus giving the CQMI an operational interpretation in terms of a state deconstruction protocol. We also define a related task called conditional erasure, in which the goal is to apply noise to systems $AE$ in order to decouple system $A$ from systems $BE$, while causing negligible disturbance to the marginal state of systems $BE$. We find that the optimal rate of noise for conditional erasure is also equal to the CQMI $I(A;B|E)$. State deconstruction and conditional erasure lead to operational interpretations of quantum discord and squashed entanglement. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C52.00012: Experimentally Generated Random Numbers Certified by the Impossibility of Superluminal Signaling Peter Bierhorst, Lynden K. Shalm, Alan Mink, Stephen Jordan, Yi-Kai Liu, Andrea Rommal, Scott Glancy, Bradley Christensen, Sae Woo Nam, Emanuel Knill Random numbers are an important resource for applications such as numerical simulation and secure communication. However, it is difficult to certify whether a physical random number generator is truly unpredictable. Here, we exploit the phenomenon of quantum nonlocality in a loophole-free photonic Bell test experiment to obtain data containing randomness that cannot be predicted by any theory that does not also allow the sending of signals faster than the speed of light. To certify and quantify the randomness, we develop a new protocol that performs well in an experimental regime characterized by low violation of Bell inequalities. Applying an extractor function to our data, we obtain 256 new random bits, uniform to within $10^-3$. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C52.00013: Heralding single photons with cascaded downconversion Deny Hamel, Patrick Poitras, Evan Meyer-Scott Heralded single photon sources are an enabling resource for several important quantum technologies such as secure communication and randomness generation. They are commonly implemented employing photon pairs from spontaneous parametric downconversion by using the detection of photon to herald the presence of this partner, but the quality of such sources is constrained by detector dark counts and double pair emission. In this work, we investigate whether photon precertification, which has recently been implement with cascaded downconversion, could help mitigate these limitations by providing an additional trigger signal confirming the arrival of the single photons. We find that, for certain regimes of detector performance, our method produces higher purity single photons as quantified by the second order correlation function. We expect these results to be of particular interest for applications where the purity of single photons, rather than the count rate, is paramount. [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C52.00014: Indistinguishability as non-locality constraint Cassio S. Amorim Quantum mechanics has long bewildered many people and questionings about its consistency and completeness have been raised, such as the famous case of the Einstein-Podolsky-Rosen paradox. Nonetheless, quantum theory has established firm grounds for our understanding about microscopic phenomena, and non-locality and entanglement is nowadays considered an important resource for quantum information processing. However, it has been noticed that relativistic causality and non-locality alone, assumed as axioms, are not enough to explain the limit of two-qubit quantum correlations, known as Tsirelson's bound. In this paper, to obtain such explanation, indistinguishability is added as a fundamental principle to these two axioms set, standing as the source of interaction and correlation. Taken together, the three principles --- no-signaling, non-locality, and indistinguishability --- can reproduce Tsirelson's bound and offer a simple and elegant explanation to non-local quantum correlations. [Preview Abstract] |
Monday, March 13, 2017 5:18PM - 5:30PM |
C52.00015: Local Discrimination with One-way Communication of Bipartite Orthogonal Quantum States Alvin Gonzales, Eric Chitambar Quantum state discrimination is a fundamental problem in quantum communication. We investigate the optimal distinguishability of orthogonal bipartite quantum states. The scenario consists of three parties: Alice, Bob, and Charlie. Charlie prepares one of two orthogonal states and sends one qubit to Alice and the other to Bob. Their goal is to correctly identify which state Charlie sends. In most state discrimination scenarios it is assumed that Alice and Bob can freely communicate with one another. In this talk, we consider a more restricted setting where only one-way communication is allowed. Consequently, Alice and Bob might differ in guessing which state Charlie distributes. When the communication is from Alice to Bob, there are two figures of merit: (i) Alice's greatest probability of identifying the state, and (ii) Bob's greatest probability of identifying the state when assisted by Alice's communication. The question we consider is whether both of these optimal probabilities can be simultaneously obtained. We show that in general they cannot. In other words, sometimes Alice must sacrifice knowledge to optimize Bob's chances of distinguishing the states. In the worst case scenario, Alice's ability to distinguish correctly shrinks from 100\% to 50\%. [Preview Abstract] |
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