CQT Colloquium by Alexander Lvovsky, University of Oxford

Title: Optics and neural networks working together
Date/Time: 22-Jun, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract:Optics and machine learning are natural symbionts. I will present three examples of how these fields can benefit each other based on our recent experimental work:

• Optical neural networks and their all-optical training;
• Robotic alignment of optical experiments;
• Application of machine learning in linear-optical far-field super resolution imaging

CQT Talk by Jinzhao Wang, Stanford University

Title: Some information-theoretic fine prints on the Bekenstein bound
Date/Time: 14-Jul, 03:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract: The Bekenstein bound posits a maximum entropy of matter that is of finite energy and confined in a region. It’s often interpreted as a fundamental limit of the information carried by physical objects. In this work, we examine this interpretation by asking if the Bekenstein bound imposes constraints on the channel capacity of communication in spacetime, a scenario in which information can be put on a mathematically rigorous and operationally meaningful footing. Specifically, we study the ``Unruh channel’’ that describes a stationary Alice sending information by exciting different species of free scalar fields to an accelerating Bob, who is confined in a Rindler wedge and is exposed to the noise of Unruh radiation. We show that the unassisted classical capacity of the Unruh channel obeys the Bekenstein bound, and it asymptotes to some small constant value at the large temperature limit. Surprisingly, however, the entanglement-assisted classical capacity is as large as the input dimension (i.e. the number of species) even in arbitrarily hot Unruh radiation. Such separation also shows up for quantum capacities.

To better understand this phenomenon, we directly examine the error recoverability of the Unruh channel and find that, irrespective of the input dimension, it always preserves well the fidelity for any pair of codewords. It hints that the Unruh channel is capable of sending ``zero-bits’’ with an error that doesn’t scale worse with the number of species. Zero-bits are communication resources that can be used as the minimal substitute for the classical/quantum bits needed for many primitive information processing protocols, such as dense coding and teleportation.  We then show a stronger result that the Unruh channel has a large zero-bit capacity even at the infinite temperature limit, which explains the capacity boost with entanglement assistance. Therefore, unlike bits and qubits, zero-bits and their associated information processing capability are not constrained by the Bekenstein bound. (Based on joint work with Patrick Hayden.)

CQT Talk by Andre Nies, University of Auckland

Title: From MIP*=RE to the Connes embedding conjecture via logic (work of Goldbring and Hart)
Date/Time: 21-Jun, 03:00PM
Venue: CQT Level 5 Seminar Room, S15-05-14

Abstract:Isaac Goldbring and Bradd Hart  proved in 2016  that the Connes embedding conjecture implies that the universal theory of the hyperfinite II_1 factor R (a fragment of  continuous logic)  is decidable. In more recent work, they used this prove undecidability of this theory  from the core result of the MIP*=RE,   the undecidability of the value of nonlocal games, thus giving a shortcut to the refutation of the conjecture.   The end of the talk  will speculate about connections to the Martin-Loef random quantum states of the speaker and Scholz. We will endeavour to explain all technical notions during the talk.
References:
I. Goldbring and B. Hart, Computability and the Connes embedding problem, Bull. Symb. Log. 22 (2016), no. 2, 238–248, DOI 10.1017/bsl.2016.5. MR3532694
I. Goldbring  and B.  Hart. "The universal theory of the hyperfinite II_1  factor is not computable." arXiv preprint arXiv:2006.05629 (2020).
A. Nies, André and V. Scholz. "Martin-Löf random quantum states." Journal of Mathematical Physics 60, no. 9 (2019): 092201.

CQT Colloquium by Jon Allcock, Tencent

Title: TensorCircuit: A quantum software framework for the NISQ era
Date/Time: 08-Jun, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract:We give an overview of TensorCircuit, a new open source quantum circuit simulator based on tensor network contraction, and built on top of industry-standard machine learning frameworks. It supports automatic differentiation, just-in-time compilation, vectorized parallelism and hardware acceleration, which allow researchers to simulate larger and more complex quantum circuits than existing simulators, and make it especially suited to variational algorithms based on parameterized quantum circuits as well as hybrid quantum-classical neural networks.

CQT Colloquium by Mark Hillery, Hunter College

Title: Developments in Wave-Particle Duality
Date/Time: 17-Aug, 04:00PM
Venue: CQT Level 3 Seminar Room, S15-03-15

Abstract:Wave-particle duality is one of the fundamental features of quantum mechanics.  This was formalized by a number of duality relations that  quantified wave and particle behavior and showed that their total cannot exceed a particular limit.  Recently, the resource theory of quantum coherence has given us new ways of quantifying wave behavior, and these have been incorporated into new duality relations.  These coherence measures have operational meanings.  Some of the duality relations can be formulated as games.  Finally, it is possible to make measurements that provide partial wave and particle information, and we formulate limitations on how much total information can be extracted by these measurements.