Format results

Talk

Gravity Dual of Quantum Information Metric
Tadashi Takayanagi Yukawa Institute for Theoretical Physics

A new perspective on holographic entanglement
Matthew Headrick Brandeis University

Universal holographic description of CFT entanglement entropy
Thomas Faulkner University of Illinois UrbanaChampaign

Geometric Constructs in AdS/CFT
Veronika Hubeny University of California, Davis

Do black holes create polyamory
Jonathan Oppenheim University College London

Tensor Network Renormalization and the MERA
Glen Evenbly Georgia Institute of Technology

Entanglement renormalization for quantum fields
Jutho Haegeman Ghent University

Holographic quantum errorcorrecting codes: Toy models for the bulk/boundary correspondence
Fernando Pastawski California Institute of Technology



Restricted Boltzmann Machines (RBMs)
Mohamed Hibat Allah Perimeter Institute for Theoretical Physics


CircuittoHamiltonian from tensor networks and fault tolerance
Quynh Nguyen Harvard University

sordered phasespace correspondences, fermions, and negativities
Ninnat Dangniam Naresuan University

Nonclassicality in correlations without causal order
Ravi Kunjwal AixMarseille University

Randomly Monitored Quantum Codes
Dongjin Lee Perimeter Institute for Theoretical Physics



Quantum metrological limits in noisy environments
Sisi Zhou Perimeter Institute for Theoretical Physics


Quantum Information in Quantum Gravity II
Quantum Information in Quantum Gravity II 
Separability as a window into manybody mixedstate phases
Tarun Grover UC San Diego
Ground states as well as Gibbs states of manybody quantum Hamiltonians have been studied extensively for some time. In contrast, the landscape of mixed states that do not correspond to a system in thermal equilibrium is relatively less explored. In this talk I will motivate a rather coarse characterization of mixed quantum manybody states using the idea of "separability", i.e., whether a mixed state can be expressed as an ensemble of shortrange entangled pure states. I will discuss several examples of decoherencedriven phase transitions from a separability viewpoint, and argue that such a framework also provides a potentially new view on Gibbs states. Based on work with YuHsueh Chen. References: 2309.11879, 2310.07286, 2403.06553. 
Restricted Boltzmann Machines (RBMs)
Mohamed Hibat Allah Perimeter Institute for Theoretical Physics


CircuittoHamiltonian from tensor networks and fault tolerance
Quynh Nguyen Harvard University
We define a map from an arbitrary quantum circuit to a local Hamiltonian whose ground state encodes the quantum computation. All previous maps relied on the FeynmanKitaev construction, which introduces an ancillary ‘clock register’ to track the computational steps. Our construction, on the other hand, relies on injective tensor networks with associated parent Hamiltonians, avoiding the introduction of a clock register. This comes at the cost of the ground state containing only a noisy version of the quantum computation, with independent stochastic noise. We can remedy this  making our construction robust  by using quantum fault tolerance. In addition to the stochastic noise, we show that any state with energy density exponentially small in the circuit depth encodes a noisy version of the quantum computation with adversarial noise. We also show that any ‘combinatorial state’ with energy density polynomially small in depth encodes the quantum computation with adversarial noise. This serves as evidence that any state with energy density polynomially small in depth has a similar property. As an application, we give a new proof of the QMAcompleteness of the local Hamiltonian problem (with logarithmic locality) and show that contracting injective tensor networks to additive error is BQP hard. We also discuss the implication of our construction to the quantum PCP conjecture, combining with an observation that QMA verification can be done in logarithmic depth. Based on joint work with Anurag Anshu and Nikolas P. Breuckmann. (https://arxiv.org/abs/2309.16475)


sordered phasespace correspondences, fermions, and negativities
Ninnat Dangniam Naresuan University
For continuousvariable systems, the negativities in the sparametrized family of quasiprobability representations on a classical phase space establish a sort of hierarchy of nonclassility measures. The coherent states, by design, display no negativity for any value of 1≤s≤1, meaning that sampling from the quantum probability distribution resulting from any measurement of a coherent state can be classically simulated, placing the coherent states as the most classical states according to this particular choice of phase space.
In this talk, I will describe how to construct sordered quasiprobability representations for finitedimensional quantum systems when the phase space is equipped with more general group symmetries, focusing on the fermionic SO(2n) symmetry. Along the way, I will comment on an obstruction to an analogue of Hudson's theorem, namely that the only pure states that have positive s=0 Wigner functions are Gaussian states, and a possible remedy by giving up linearity in the phasespace correspondence.


Nonclassicality in correlations without causal order
Ravi Kunjwal AixMarseille University
A Bell scenario can be conceptualized as a "communication" scenario with zero rounds of communication between parties, i.e., although each party can receive a system from its environment on which it can implement a measurement, it cannot send out any system to another party. Under this constraint, there is a strict hierarchy of correlation sets, namely, classical, quantum, and nonsignalling. However, without any constraints on the number of communication rounds between the parties, they can realize arbitrary correlations by exchanging only classical systems. We consider a multipartite scenario where the parties can engage in at most a single round of communication, i.e., each party is allowed to receive a system once, implement any local intervention on it, and send out the resulting system once. Taking our cue from Bell nonlocality in the "zero rounds" scenario, we propose a notion of nonclassicalitytermed antinomicityfor correlations in scenarios with a single round of communication. Similar to the zero rounds case, we establish a strict hierarchy of correlation sets classified by their antinomicity in singleround communication scenarios. Since we do not assume a global causal order between the parties, antinomicity serves as a notion of nonclassicality in the presence of indefinite causal order (as witnessed by causal inequality violations). A key contribution of this work is an explicit antinomicity witness that goes beyond causal inequalities, inspired by a modification of the Guess Your Neighbour's Input (GYNI) game that we term the Guess Your Neighbour's Input or NOT (GYNIN) game. Time permitting, I will speculate on why antinomicity is a strong notion of nonclassicality by interpreting it as an example of finetuning in classical models of indefinite causality.This is based on joint work with Ognyan Oreshkov, arXiv:2307.02565.


Randomly Monitored Quantum Codes
Dongjin Lee Perimeter Institute for Theoretical Physics
Quantum measurement has conventionally been regarded as the final step in quantum information processing, which is essential for reading out the processed information but collapses the quantum state into a classical state. However, recent studies have shown that quantum measurement itself can induce novel quantum phenomena. One seminal example is a monitored random circuit, which can generate longrange entanglement faster than a random unitary circuit. Inspired by these results, in this talk, we address the following question: When quantum information is encoded in a quantum errorcorrecting code, how many physical qubits should be randomly measured to destroy the encoded information? We investigate this question for various quantum errorcorrecting codes and derive the necessary and sufficient conditions for destroying the information through measurements. In particular, we demonstrate that for a large class of quantum errorcorrecting codes, it is impossible to destroy the encoded information through random singlequbit Pauli measurements when a tiny portion of physical qubits is still unmeasured. Our results not only reveal the extraordinary robustness of quantum codes under measurement decoherence, but also suggest potential applications in quantum information processing tasks.


The how and why of translating between the circuit model and the oneway model of quantum computing
Miriam Backens Université de Lorraine
In the oneway model of measurement based quantum computing, unlike the quantum circuit model, a computation is driven not by unitary gates but by successive adaptive singlequbit measurements on an entangled resource state. Socalled flow properties ensure that a oneway computation, described by a measurement pattern, is deterministic overall (up to Pauli corrections on output qubits). Translations between quantum circuits and measurement patterns have been used to show universality of the oneway model, verify measurement patterns, optimise quantum circuits, and more. Yet while it is straightforward to translate a circuit into a measurement pattern, the question of algorithmic "circuit extraction"  how to translate general measurement patterns with flow to ancillafree circuits  had long remained open for all but the simplest type of flow. In this talk, we will recap the oneway model of quantum computing and then explain how the problem of circuit extraction was resolved using the ZXcalculus as a common language for circuits and measurement patterns. We also discuss applications. 
GOLDPLATED SICS
Ingemar Bengtsson University of Stockholm
There are well established conjectures about the symmetries of SICPOVMs, and the number fields needed to construct them. If the dimension is of the form n^2 + 3 there is also an algorithm that allows us to calculate them, making use of Stark units in a subfield of the full number field. The algorithm works in the 72 dimensions where it has been tested. Joint work with (among others) Markus Grassl and Gary McConnell 
Quantum metrological limits in noisy environments
Sisi Zhou Perimeter Institute for Theoretical Physics
The Heisenberg limit (HL) and the standard quantum limit (SQL) are two fundamental quantum metrological limits, which describe the scalings of estimation precision of an unknown parameter with respect to N, the number of oneparameter quantum channels applied. In the first part, we show the HL (1/N) is achievable using quantum error correction (QEC) strategies when the ``HamiltoniannotinKrausspan'' (HNKS) condition is satisfied; and when HNKS is violated, the SQL (1/N^1/2) is optimal and can be achieved with repeated measurements. In the second part, we identify modified metrological limits for estimating oneparameter qubit channels in settings of restricted controls where QEC cannot be performed. We prove unattainability of the HL and further show a ``rotationgeneratorsnotinKrausspan'' (RGNKS) condition that determines the achievability of the SQL. 
Probing the limits of classical computing with arbitrarily connected quantum circuits
Michael FossFeig Quantinuum
Empirical evidence for a gap between the computational powers of classical and quantum computers has been provided by experiments that sample the output distribution of twodimensional quantum circuits. Many attempts to close this gap have utilized classical simulations based on tensor network techniques, and their limitations shed light on the improvements to quantum hardware required to inhibit classical simulability. In particular, state of the art quantum computers having in excess of ~50 qubits are primarily vulnerable to classical simulation due to restrictions on their gate fidelity and their connectivity, the latter determining how many gates are required (and therefore how much infidelity is suffered) in generating highlyentangled states. Here, we describe numerical evidence for the difficulty of random circuit sampling in highly connected geometries.