Information Causality, Szemerédi-Trotter and Algebraic Variants of CHSH

In this paper, we consider the following family of two prover one-round games. In the CHSH q game, two parties are given x; y F q uniformly at random, and each must produce an output a; b F q without communicating with the other. The players' objective is to maximize the probability that their outputs satisfy a + b = xy in F q . This game was introduced by Buhrman and Massar [7] as a large alphabet generalization of the CHSH game-which is one of the most well-studied two-prover games in quantum information theory, and which has a large number of applications to quantum cryptography and quantum complexity. Our main contributions in this paper are the first asymptotic and explicit bounds on the entangled and classical values of CHSH q , and the realization of a rather surprising connection between CHSH q and geometric incidence theory.National Science Foundation (U.S.). Science and Technology Center (Award 0939370)National Science Foundation (U.S.) (grant CCF-0829421)National Science Foundation (U.S.).(CCF-1065125)National Science Foundation (U.S.).(grant CCF-0939370

Quantum and superquantum enhancements to two-sender, two-receiver channels

We study the consequences of superquantum nonlocal correlations as represented by the PR-box model of Popescu and Rohrlich, and show that PR boxes can enhance the capacity of noisy interference channels between two senders and two receivers. PR-box correlations violate Bell and CHSH inequalities and are thus stronger—more nonlocal—than quantum mechanics, yet weak enough to respect special relativity in prohibiting faster-than-light communication. Understanding their power will yield insight into the nonlocality of quantum mechanics. We exhibit two proof-of-concept channels: First, we show a channel between two sender-receiver pairs where the senders are not allowed to communicate, for which a shared superquantum bit (a PR box) allows perfect communication. This feat is not achievable with the best classical (senders share no resources) or quantum-entanglement-assisted (senders share entanglement) strategies. Second, we demonstrate a class of channels for which a tunable parameter ε achieves a double separation of capacities; for some range of ε, the superquantum-assisted strategy does better than the entanglement-assisted strategy, which in turn does better than the classical one.National Science Foundation (U.S.) (CCF-121-8176)National Science Foundation (U.S.) (CCF0-939370

Additive Classical Capacity of Quantum Channels Assisted by Noisy Entanglement

We give a capacity formula for the classical information transmission over a noisy quantum channel, with separable encoding by the sender and limited resources provided by the receiver’s preshared ancilla. Instead of a pure state, we consider the signal-ancilla pair in a mixed state, purified by a “witness.” Thus, the signal-witness correlation limits the resource available from the signal-ancilla correlation. Our formula characterizes the utility of different forms of resources, including noisy or limited entanglement assistance, for classical communication. With separable encoding, the sender’s signals across multiple channel uses are still allowed to be entangled, yet our capacity formula is additive. In particular, for generalized covariant channels, our capacity formula has a simple closed form. Moreover, our additive capacity formula upper bounds the general coherent attack’s information gain in various two-way quantum key distribution protocols. For Gaussian protocols, the additivity of the formula indicates that the collective Gaussian attack is the most powerful.United States. Air Force. Office of Scientific Research (Grant FA9550-14-1-0052)Massachusetts Institute of Technology. Research Laboratory of Electronics (Claude E. Shannon Fellowship)National Science Foundation (U.S.) (Grant CCF-1525130)National Science Foundation (U.S.) (Center for Science of Information. Grant CCF0-939370

New Constructions of Codes for Asymmetric Channels via Concatenation

We present new constructions of codes for asymmetric channels for both binary and nonbinary alphabets, based on methods of generalized code concatenation. For the binary asymmetric channel, our methods construct nonlinear single-error-correcting codes from ternary outer codes. We show that some of the Varshamov-Tenengol'ts-Constantin-Rao codes, a class of binary nonlinear codes for this channel, have a nice structure when viewed as ternary codes. In many cases, our ternary construction yields even better codes. For the nonbinary asymmetric channel, our methods construct linear codes for many lengths and distances which are superior to the linear codes of the same length capable of correcting the same number of symmetric errors

Entropy Bound for the Classical Capacity of a Quantum Channel Assisted by Classical Feedback

We prove that the classical capacity of an arbitrary quantum channel assisted by a free classical feedback channel is bounded from above by the maximum average output entropy of the quantum channel. As a consequence of this bound, we conclude that a classical feedback channel does not improve the classical capacity of a quantum erasure channel, and by taking into account energy constraints, we conclude the same for a pure-loss bosonic channel. The method for establishing the aforementioned entropy bound involves identifying an information measure having two key properties: 1) it does not increase under a one-way local operations and classical communication channel from the receiver to the sender and 2) a quantum channel from sender to receiver cannot increase the information measure by more than the maximum output entropy of the channel. This information measure can be understood as the sum of two terms, with one corresponding to classical correlation and the other to entanglement.National Science Foundation (U.S.) (Grant CCF-1525130)National Science Foundation (U.S.). Science Technology Center for Science of Information (Grant CCF0-939370

Random planar matching and bin packing

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1985.Bibliography: leaves 123-124.by Peter Williston Shor.Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 1985

Superadditivity in trade-off capacities of quantum channels

In this paper, we investigate the additivity phenomenon in the quantum dynamic capacity region of a quantum channel for trading the resources of classical communication, quantum communication, and entanglement. Understanding such an additivity property is important if we want to optimally use a quantum channel for general communication purposes. However, in a lot of cases, the channel one will be using only has an additive single or double resource capacity region, and it is largely unknown if this could lead to a strictly superadditive double or triple resource capacity region, respectively. For example, if a channel has additive classical and quantum capacities, can the classical-quantum capacity region be strictly superadditive? In this paper, we answer such questions affirmatively. We give proof-of-principle requirements for these channels to exist. In most cases, we can provide an explicit construction of these quantum channels. The existence of these superadditive phenomena is surprising in contrast to the result that the additivity of both classical-entanglement and classical-quantum capacity regions imply the additivity of the triple resource capacity region for a given channel

Polylog-LDPC Capacity Achieving Codes for the Noisy Quantum Erasure Channel

We provide polylog sparse quantum codes for correcting the erasure channel arbitrarily close to the capacity. Specifically, we provide [[n, k, d]] quantum stabilizer codes that correct for the erasure channel arbitrarily close to the capacity if the erasure probability is at least 0.33, and with a generating set hS1, S2, . . . Sn−ki such that |Si | ≤ log2+ζ (n) for all i and for any ζ > 0 with high probability. In this work we show that the result of Delfosse et al. [5] is tight: one can construct capacity approaching codes with weight almost O(1)

Superadditivity in Trade-Off Capacities of Quantum Channels

© 2018 IEEE. We investigate the additivity phenomenon in the dynamic capacity of a quantum channel for trading the resources of classical communication, quantum communication, and entanglement. Understanding such an additivity property is important if we want to optimally use a quantum channel for general communication purposes. However, in a lot of cases, the channel one will be using only has an additive single or double resource capacity, and it is largely unknown if this could lead to an superadditive double or triple resource capacity, respectively. For example, if a channel has an additive classical and quantum capacity, can the classical-quantum capacity be superadditive? In this work, we answer such questions affirmatively. We give proof-of-principle requirements for these channels to exist. In most cases, we can provide an explicit construction of these quantum channels. The existence of these superadditive phenomena is surprising in contrast to the result that the additivity of both classical-entanglement and classical-quantum capacity regions imply the additivity of the triple resource capacity region