Format results



An SYK model with a scaling similarity.
Juan Maldacena Institute for Advanced Study (IAS)  School of Natural Sciences (SNS)

Talk 61  Horizons are Watching You
Gautam Satishchandran 
Talk 124  von Neumann algebras in JT gravity with matter
David Kolchmeyer Massachusetts Institute of Technology

Talk 88  Type II_1 algebras for local subregions in quantum gravity
Antony Speranza University of Illinois UrbanaChampaign

Talk 44  Large N von Neumann Algebras and the renormalization of Newton's constant
Elliott Gesteau California Institute of Technology (Caltech)

Talk


QPV: An Overview and Reflections
Harry Buhrman Centrum Wiskunde & Informatica

PopescuRohrlich correlations imply efficient instantaneous nonlocal quantum computation
Anne Broadbent University of Ottawa
PIRSA:23090023 
Nonlocal quantum computation meets quantum gravity
Alex May Perimeter Institute for Theoretical Physics

Quantum ErrorCorrection and Holographic Task
Beni Yoshida Perimeter Institute for Theoretical Physics


Protocols and Implementations of Quantum Position Verification

Eric Chitamber University of Illinois

Paul Kwiat University of Illinois





The minentropy of classical quantum combs and some applications
Isaac Smith LeopoldFranzens Universität Innsbruck

Testing quantum states
Mehdi Soleimanifar California Institute of Technology (Caltech)

Measurement Quantum Cellular Automata and Anomalies in Floquet Codes
Zhi Li Perimeter Institute for Theoretical Physics

Talk 41  Mutual Information of Holographic Generalized Free Fields
Pedro Jorge Martinez Instituto Balseiro
We study Generalized Free Fields (GFF) from the point of view of information measures. We begin by reviewing conformal GFF, their holographic representation, and the multiple possible assignations of algebras to a single spacetime region that arise in these theories. We will focus on manifestations of these features present in the Mutual Information (MI) of holographic GFF. First, we show that the MI can be expected to be finite even if the AdS dual space is of infinite volume. Then, we present the longdistance limit of the MI for regions with arbitrary boundaries in the light cone for the causal and entanglement wedge algebras. The pinching limit of these surfaces shows the GFF behaves as an interacting model from the MI point of view. The entanglement wedge algebra choice allows these models to ``fake'' causality, giving results consistent with their role in the description of large N models. Finally, we explore the short distance limit of the MI. Interestingly, we find that the GFF has a leading volume term rather than an area term and a logarithmic term in any dimension rather than only for even dimensions as in ordinary CFTs. We also find the dependence of some subleading terms on the conformal dimension of the GFF. 
Talk 67  Irreversibility, QNEC, and defects
In this talk, we will first present an analysis of infinitesimal null deformations for the entanglement entropy, which leads to a major simplification of the proof of the C, F and Atheorems in quantum field theory. Next, we will discuss the quantum null energy condition (QNEC) on the lightcone. Finally, we combine these tools in order to establish the irreversibility of renormalization group flows on planar ddimensional defects, embedded in Ddimensional conformal field theories. This proof completes and unifies all known defect irreversibility theorems for defect dimensions below d=5. The Ftheorem on defects (d=3) is a new result using informationtheoretic methods. The geometric construction connects the proof of irreversibility with and without defects through the QNEC inequality in the bulk, and makes contact with the proof of strong subadditivity of holographic entropy taking into account quantum corrections. 
An SYK model with a scaling similarity.
Juan Maldacena Institute for Advanced Study (IAS)  School of Natural Sciences (SNS)
We describe supersymmetric SYK models which display a scaling similarity at low temperatures, rather than the usual conformal behavior. We discuss the large N equations, which were studied previously as uncontrolled approximations to other models. We also present a picture for the physics of the model which suggest that the relevant low energy degrees of freedom are almost free. We also searched for a spin glass phase but we found no replica symmetry breaking solutions. 
Talk 61  Horizons are Watching You
Gautam SatishchandranWe show that if a massive (or charged) body is put in a quantum superposition of spatially separated states in the vicinity of any (Killing) horizon, the mere presence of the horizon will eventually destroy the coherence of the superposition in a finite time. This occurs because, in effect, the longrange fields sourced by the superposition register on the black hole horizon which forces the emission of entangling “soft gravitons/photons” through the horizon. This enables the horizon to harvest “which path” information about the superposition. We provide estimates of the decoherence time for such quantum superpositions in the presence of a black hole and cosmological horizon. Finally, we further sharpen and generalize this mechanism by recasting the gedankenexperiment in the language of (approximate) quantum error correction. This yields a complementary picture where the decoherence is due to an “eavesdropper” (Eve) in the black hole attempting to obtain "which path" information by measuring the longrange fields of the superposed body. We explicitly compute the quantum fidelity to determine the amount of information such an Eve can obtain and show, by the informationdisturbance tradeoff, a direct relationship between the information gained by Eve and the decoherence of the superposition in the exterior. In particular, we show that the decoherence of the superposition corresponds to the "optimal" measurement made by Eve in the black hole interior. 
Talk 124  von Neumann algebras in JT gravity with matter
David Kolchmeyer Massachusetts Institute of Technology
We quantize JT gravity with matter on the spatial interval with two asymptotically AdS boundaries. We consider the von Neumann algebra generated by the right Hamiltonian and the gravitationally dressed matter operators on the right boundary. We prove that the commutant of this algebra is the analogously defined left boundary algebra and that both algebras are type II infinity factors. These algebras provide a precise notion of the entanglement wedge away from the semiclassical limit. 
Talk 88  Type II_1 algebras for local subregions in quantum gravity
Antony Speranza University of Illinois UrbanaChampaign
We argue that generic local subregions in semiclassical quantum gravity are associated with von Neumann algebras of type II_1, extending recent work by Chandrasekaran et.al. beyond subregions bounded by Killing horizons. The subregion algebra arises as a crossed product of the type III_1 algebra of quantum fields in the subregion by the flow generated by a gravitational constraint operator. We conjecture that this flow agrees with the vacuum modular flow sufficiently well to conclude that the resulting algebra is type II_\infty, which projects to a type II_1 algebra after imposing a positive energy condition. The entropy of semiclassical states on this algebra can be computed and shown to agree with the generalized entropy by appealing to a first law of local subregions. The existence of a maximal entropy state for the type II_1 algebra is further shown to imply a version of Jacobson’s entanglement equilibrium hypothesis. We discuss other applications of this construction to quantum gravity and holography, including the quantum extremal surface prescription and the quantum focusing conjecture. 
Talk 44  Large N von Neumann Algebras and the renormalization of Newton's constant
Elliott Gesteau California Institute of Technology (Caltech)
In holography, the quantum extremal surface formula relates the entropy of a boundary state to the sum of two terms: the area term and the entropy of bulk fields inside the entanglement wedge. As the bulk effective field theory suffers from UV divergences, the second term must be regularized. It has been conjectured since the work of Susskind and Uglum that the renormalization of Newton’s constant in the area term exactly cancels the difference between different choices of regularization for bulk entropy. In this talk, I will explain how the recent developments on von Neumann algebras appearing in the large N limit of holography allow to prove this claim within the framework of holographic quantum error correction, and to reinterpret it as an instance of the ER=EPR paradigm. This talk is based on the paper arXiv:2302.01938. 
QPV 2023: Advances in quantum position verification
Quantum position verification (QPV) schemes use the properties of quantum information and the relativistic signalling bound to verify the location of an object (sometimes called a “tag”) to distant observers in an environment that may contain wouldbe spoofers. The guarantee is based on the assumptions of the underlying security model; various theoretically and practically interesting security models have been proposed. The area is attracting increasing interest, with new theoretical developments in security analyses, emerging experimental studies of QPV systems, and recently discovered surprising and intriguing connections to topics in quantum gravity. A workshop on QPV will be held at the Perimeter Institute for Theoretical Physics.
The workshop will cover topics related to all aspects of QPV, including, but not limited to:
 Theoretical developments related to the security of QPV schemes, including development or refinement of security models, proofs of security within given models, tradeoffs between security and efficiency, and Experimental studies of QPV and theoretical work aimed at developing practical QPV schemes.
 QPV’s relationship to other cryptographic tasks and primitives.
 QPV’s relationship to holography and quantum gravity.
Territorial Land Acknowledgement
Perimeter Institute acknowledges that it is situated on the traditional territory of the Anishinaabe, Haudenosaunee, and Neutral peoples.
Perimeter Institute is located on the Haldimand Tract. After the American Revolution, the tract was granted by the British to the Six Nations of the Grand River and the Mississaugas of the Credit First Nation as compensation for their role in the war and for the loss of their traditional lands in upstate New York. Of the 950,000 acres granted to the Haudenosaunee, less than 5 percent remains Six Nations land. Only 6,100 acres remain Mississaugas of the Credit land.
We thank the Anishinaabe, Haudenosaunee, and Neutral peoples for hosting us on their land.

Dissipative Quantum Gibbs Sampling
Daniel Zhang Phasecraft
Systems in thermal equilibrium at nonzero temperature are described by their Gibbs state. For classical manybody systems, the MetropolisHastings algorithm gives a Markov process with a local update rule that samples from the Gibbs distribution. For quantum systems, sampling from the Gibbs state is significantly more challenging. Many algorithms have been proposed, but these are more complex than the simple local update rule of classical Metropolis sampling, requiring nontrivial quantum algorithms such as phase estimation as a subroutine.
Here, we show that a dissipative quantum algorithm with a simple, local update rule is able to sample from the quantum Gibbs state. In contrast to the classical case, the quantum Gibbs state is not generated by converging to the fixed point of a Markov process, but by the states generated at the stopping time of a conditionally stopped process. This gives a new answer to the longsoughtafter quantum analogue of Metropolis sampling. Compared to previous quantum Gibbs sampling algorithms, the local update rule of the process has a simple implementation, which may make it more amenable to nearterm implementation on suitable quantum hardware. We also show how this can be used to estimate partition functions using the stopping statistics of an ensemble of runs of the dissipative Gibbs sampler. This dissipative Gibbs sampler works for arbitrary quantum Hamiltonians, without any assumptions on or knowledge of its properties, and comes with certifiable precision and runtime bounds.
This talk is based on 2304.04526, completed in collaboration with JanLukas Bosse and Toby Cubitt.Zoom Link: https://pitp.zoom.us/j/96780945341?pwd=NG9SUjE4SkVia3VqazNXUFNUamhRdz09

The minentropy of classical quantum combs and some applications
Isaac Smith LeopoldFranzens Universität Innsbruck
It is often the case that interaction with a quantum system does not simply occur between an initial point in time and a final one, but rather over many time steps. In such cases, an interaction at a given time step can have an influence on the dynamics of the system at a much later time. Just as quantum channels model dynamics between two time steps, quantum combs model the more general multitime dynamics described above, and have accordingly found application in such fields as open quantum systems and quantum cryptography. In this talk, we will consider ensembles of combs indexed by a random variable, dubbed classicalquantum combs, and discuss how much can be learnt about said variable through interacting with the system. We characterise the amount of information gain using the comb minentropy, an extension of the analogous entropic quantity for quantum states. With combs and the minentropy in our toolbox, we turn to a number of applications largely inspired by MeasurementBased Quantum Computing (MBQC), including the security analysis of a specific Blind Quantum Computing protocol and some comments regarding learning causal structure.
Zoom Link: https://pitp.zoom.us/j/98315660866?pwd=cWU3RzB6SG9DOGIza1BqV1lqNklvQT09

Testing quantum states
Mehdi Soleimanifar California Institute of Technology (Caltech)
In this talk, I will present three algorithms that address distinct variants of the problem of testing quantum states. First, I will discuss the problem of statistically testing whether an unknown quantum state is a matrix product state of certain bond dimension or it is far from all such states. Next, I will demonstrate a method for testing whether a bipartite quantum state, shared between two parties, corresponds to the ground state of a given gapped local Hamiltonian. Finally, I will present a scheme for verifying that a machine learning model of an unknown quantum state has high overlap with the actual state.
Zoom Link: https://pitp.zoom.us/j/99250127489?pwd=UCtXUi9zMzJZamppT29DbWtJcWU3Zz09

Measurement Quantum Cellular Automata and Anomalies in Floquet Codes
Zhi Li Perimeter Institute for Theoretical Physics
We investigate the evolution of quantum information under Pauli measurement circuits. We focus on the case of one and twodimensional systems, which are relevant to the recently introduced Floquet topological codes. We define local reversibility in context of measurement circuits, which allows us to treat finite depth measurement circuits on a similar footing to finite depth unitary circuits. In contrast to the unitary case, a finite depth locally reversible measurement sequence can implement a translation in one dimension. A locally reversible measurement sequence in two dimensions may also induce a flow of logical information along the boundary. We introduce "measurement quantum cellular automata" which unifies these ideas and define an index in one dimension to characterize the flow of logical operators. We find a Z_2 bulk invariant for Floquet topological codes which indicates an obstruction to having a trivial boundary. We prove that the HastingsHaah honeycomb code belong to a class with such obstruction, which means that any boundary must have either nonlocal dynamics, period doubled, or admits boundary flow of quantum information.
Zoom Link: https://pitp.zoom.us/j/96083249406?pwd=MnhYbTEyU05ybVdyUlE3UGZrdEhPdz09