Exploring the nonlinear dynamics of Einstein dilaton Gauss-Bonnet gravity
Justin Ripley Princeton University
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Baby Universes and Black Hole Information
Donald Marolf University of California, Santa Barbara
Toward a Quantum-Safe Future
Michele Mosca Institute for Quantum Computing (IQC)
ISCOs in AdS/CFT
David Berenstein University of California, Santa Barbara
Not All Benchmarks Are Created Equal
Robin Blume-Kohout (Sandia National Labs)Cycle Benchmarking: The New Paradigm for Assessing All Relevant Errors and Error Correlations Under Specific Quantum Operation on Large-Scale Quantum Computers
Joseph Emerson (University of Waterloo)Cross-Platform Verification of Intermediate Scale Quantum Devices with Randomized Measurements
Andreas Elben (Austrian Academy of Sciences)MIP* = RE: Putting Everything Together
Zhengfeng Ji (University of Technology Sydney)
Exploring the nonlinear dynamics of Einstein dilaton Gauss-Bonnet gravity
Justin Ripley Princeton University
We discuss several numerical and analytical studies of the modified gravity theory Einstein dilaton Gauss-Bonnet (EdGB) gravity. This class of modified gravity theories admit scalarized black hole solutions. The theory may then provide significantly different gravitational wave signatures during binary black hole merger as compared to general relativity, so that gravitational wave observations may provide new stringent constraints on EdGB gravity. The theory is also an important member of the Horndeski theories, which have been used to model theories of the early universe, including inflation and ekpyrosis. We describe our investigations of the self-consistency of EdGB gravity for spherically symmetric solutions that differ significantly from those in GR, including scalarized black hole solutions, and find that for solutions where the Gauss-Bonnet corrections to general relativity are not small, the theory no longer admits hyperbolic evolution. We discuss how an effective field theory interpretation of the equations of motion though should always guarantee (locally) hyperbolic evolution for the theory.
Baby Universes and Black Hole Information
Donald Marolf University of California, Santa Barbara
In the 1980’s, work by Coleman and by Giddings and Strominger linked the physics of spacetime wormholes to ‘baby universes’ and an ensemble of theories. We revisit such ideas, using features associated with a negative cosmological constant and asymptotically AdS boundaries to strengthen the results, introduce a change in perspective, and connect with recent replica wormhole discussions of the Page curve. A key new feature is an emphasis on the role of null states. We explore this structure in detail in simple topological models of the bulk that allow us to compute the full spectrum of associated boundary theories. We also argue that similar properties must hold in any consistent gravitational path integral.
Hosted By: Stanford University Footage Courtesy: Simons Foundation for Mathematics and Physical Sciences
Toward a Quantum-Safe Future
Michele Mosca Institute for Quantum Computing (IQC)
There has been tremendous progress in the many layers needed to realize large-scale quantum computing, from the hardware layers to the high level software. There has also been vastly increased exploration into the potentially useful applications of quantum computers, which will drive the desire to build quantum computers and make them available to users. I will describe some of my research in quantum algorithmics and quantum compiling.
The knowledge and tools developed for these positive applications give us insight into the cost of implementing quantum cryptanalysis of today's cryptographic algorithms, which is a key factor in estimating when quantum computers will be cryptographically relevant (the "collapse time"). In addition to my own estimates, I will summarize the estimates of 22 other thought leaders in quantum computing.
What quantum cryptanalysis means to an organization or a sector depends not only on the collapse time, but also on the time to migrate to quantum-safe algorithms as well as the shelf-life of information assets being protected. In recent years, we have gained increasing insight into the challenges of a wide-scale migration of existing systems. We must also be proactive as we deploy new systems. Open-source platforms, like OpenQuantumSafe and OpenQKDNetwork, are valuable resources in helping meet many of these challenges.
While awareness of the challenges and the path forward has increased immensely, there is still a long road ahead as we work together with additional stakeholders not only to prepare our digital economy to be resilient to quantum attacks, but also to make us more resilient to other threats that emerge.ISCOs in AdS/CFT
David Berenstein University of California, Santa Barbara
I describe a novel way to produce states associated to geodesic motion for classical particles in the bulk of AdS that arise from particular operator insertions at the boundary
at a fixed time. When extended to black hole setups, one can understand how to map back the geometric information of the geodesics back to
the properties of these operators. In particular, the presence of stable circular orbits in global AdS are analyzed. The classical Innermost Stable Circular Orbit
(ISCO) play an important role separating metastable state excitations from those that quickly fall in the horizon of black hole. In the dual CFT, this metastability effect must be a non-perturbative effect due to the curvature on the boundary.
Efficient Learning of Pauli Channels
Steve Flammia (University of Sydney)Pauli channels are ubiquitous in quantum information, both as a dominant noise source in many computing architectures and as a practical model for analyzing error correction and fault tolerance. Here we prove several results on efficiently learning Pauli channels, and more generally the Pauli projection of a quantum channel. We first derive a procedure for learning a Pauli channel on n qubits to a fixed relative precision with O(n 2^n) measurements. For a Pauli channel with only s nonzero error rates, we show how to learn it with only O(s n) measurements. Finally, we show that when the Pauli channel is given by a Markov field with at most k-local correlations, we can learn an entire n-qubit Pauli channel with only O(n^2 log n) measurements, which is efficient in the number of qubits. These results enable a host of applications beyond just characterizing noise in a large-scale quantum system: they pave the way to tailoring quantum codes, optimizing decoders, and customizing fault tolerance procedures to suit a particular device. Joint work with Robin Harper, Joel Wallman, and Wenjun Yu, arXiv:1907.13022, arXiv:1907.12976.Not All Benchmarks Are Created Equal
Robin Blume-Kohout (Sandia National Labs)Testbed-class quantum computers -- fully programmable 5-50 qubit systems -- have burst onto the scene in the past few years. The associated surge in funding, hype, and commercial activity has spurred interest in "benchmarks" for assessing their performance. Unsurprisingly, this has generated both a number of scientifically interesting ideas *and* a lot of confusion and kerfuffle. I will try to explain the state of play in this field -- known historically as "quantum characterization, verification, and validation (QCVV)" and more recently and generally as "quantum performance assessment" -- by briefly reviewing its history, explaining the different categories of benchmarks and characterization protocols, and identifying what they're good for. The overarching message of my talk will be these are distinct tools in a diverse toolbox -- almost every known protocol and benchmark really measures a distinct and particular thing, and we probably need *more* of them, not fewer.Cycle Benchmarking: The New Paradigm for Assessing All Relevant Errors and Error Correlations Under Specific Quantum Operation on Large-Scale Quantum Computers
Joseph Emerson (University of Waterloo)Cycle benchmarking is a new approach for scalable, complete and efficient error diagnostics that will be essential to understanding and improving quantum computing performance from the NISQ era to fault-tolerance. Cycle benchmarking is born from ideas of randomized benchmarking and exposes tomographic methods as impractical and obsolete. When combined with randomized compiling, cycle benchmarking can identify the full impact of errors and error correlations for any (parallel) gate-combination of interest. I will show cycle benchmarking data from experimental implementations on multi-qubit superconducting qubit and ion trap quantum computers revealing that: (1) in leading platforms, cross-talk and other error correlations can be much more severe than expected, even many order-of-magnitude larger than expected based on independent error models; (2) these cross-talk errors induce errors on other qubits (e.g., idling qubits) that are an order of magnitude larger than the errors on the qubits in the domain of the gate operation; and thus (3) the notion of "elementary gate error rates" is not adequate for assessing quantum computing operations and cycle benchmarking provides the tool to provide an accurate assessment. I will then discuss how the aggregate error rates measured under cycle benchmarking can be applied to provide a practical bound on the accuracy of applications in what I call the "quantum discovery regime" where quantum solutions can no longer be checked via HPCs.Cross-Platform Verification of Intermediate Scale Quantum Devices with Randomized Measurements
Andreas Elben (Austrian Academy of Sciences)Recently, protocols based on statistical correlations of randomized measurements were developed for probing and verifying engineered quantum many-body systems. After a general introduction in the context of Renyi entropies, I focus in this talk on the cross-platform verification of quantum computers and simulators by means of fidelity measurements. I show how to measure the overlap between (reduced) density matrices, and thus a (mixed-state) fidelity of two quantum states prepared on separate experimental platforms. The protocol requires only local measurements in randomized product bases and classical communication between the devices. As a proof-of-principle, I present the measurement of experiment-theory fidelities for entangled 10-qubit quantum states in a trapped ion quantum simulator. To conclude, I will present further applications of randomized measurements for probing quantities beyond standard observables, such as out-of-time-ordered correlation functions.Gravitational edge modes: From Kac-Moody charges to Poincaré networks
Daniele Pranzetti University of Udine
In this talk I revisit the canonical framework for general relativity in its connection-frame field formulation, exploiting its local holographic nature. I will show how we can understand the Gauss law, the Bianchi identity and the space diffeomorphism constraints as conservation laws for local surface charges. These charges being respectively the electric flux, the dual magnetic flux and momentum charges. Quantization of the surface charge algebra can be done in terms of Kac-Moody edge modes. This leads to an enhanced theory upgrading spin networks to tube networks carrying Virasoro representations. Taking a finite dimensional truncation of this quantization yields states of quantum geometry, dubbed `Poincaré charge networks’, which carry a representation of the 3D diffeomorphism boundary charges on top of the SU(2) fluxes and gauge transformations. This opens the possibility to have for the first time a framework where spatial diffeomorphism are represented at the quantum level. Moreover, our construction leads naturally to the picture that the relevant geometrical degrees of freedom live on boundaries, that their dynamics and the fabric of quantum space itself is encoded into their entanglement, and it is designed to offer a new setting to study the coarse-graining of gravity both at the classical and the quantum levels.
MIP* = RE: Putting Everything Together
Zhengfeng Ji (University of Technology Sydney)In this talk, we will discuss the overall framework for combining many of the techniques established in previous talks of this workshop, including the quantum low-degree test, question reduction by introspection, and answer reduction by the PCP technique. Building upon these techniques, we will construct a recursive gap-preserving compression procedure for quantum two-prover interactive proofs in the normal form and use it to give a proof of MIP* = RE.MIP* = RE Part 2: PCPs and Introspection
John Wright (Caltech)Continuing in the line of MIP* = RE talks, I will discuss two of the tools involved in the result, introspection and PCP composition, which are used to compress large MIP* protocols into small MIP* protocols. I will introduce these tools in the context of prior work with Anand Natarajan showing that MIP* contains NEEXP. Joint work with Zhengfeng Ji, Anand Natarajan, Thomas Vidick, and Henry YuenThe Algebraic Side of MIP* = RE
William Slofstra (University of Waterloo)One of the most exciting consequences of the recent MIP* = RE result by Ji, Natarajan, Vidick, Wright, and Yuen is the resolution of Connes' embedding problem (CEP). Although this problem started out as a casual question about embeddings of von Neumann algebras, it has gained prominence due to its many equivalent and independently interesting formulations in operator theory and beyond. In particular, MIP* = RE resolves the CEP by resolving Tsirelson's problem, an equivalent formulation of CEP involving quantum correlation sets. In this expository talk, I'll try to explain the connection between MIP* = RE and Connes' original problem directly, using the synchronous algebras of Helton, Meyer, Paulsen, and Satriano. I'll also explain how one of the remaining open problems on the algebraic side, the existence of a non-hyperlinear group, is related to the study of variants of MIP* with lower descriptive complexity. This talk will be aimed primarily at physicists and computer scientists, although hopefully there will be something for everyone.