arXiv subjects

Tal Schwartzman

Publications and source records attributed to Tal Schwartzman.

7 recordsLinked to original sources

arXiv2026

Multi-Boundary Many-Body Quantum Teleportation

Unlike standard quantum teleportation, many-body teleportation uses scrambling to transmit quantum information. In this protocol, initially localized information spreads over many degrees of freedom and is later refocused at the receiver by a simple coupling between the systems, followed by further many-body evolution. The protocol was developed from models of traversable wormholes in holography and has become a useful probe of scrambling. In particular, it can distinguish genuine scrambling from decoherence or noise when out-of-time-order correlators fail, and can reveal signatures of different scrambling mechanisms, including the distinctive behavior expected in holographic systems. Holography predicts that related protocols can transmit information between selected boundaries of multi-boundary wormhole geometries. Motivated by this setting, we study single-qubit many-body teleportation among three systems of qubits. The initial state consists of EPR pairs distributed among them, providing a simple analogue of an infinite-temperature three-boundary holographic state. We analyze the protocol with one-dimensional and all-to-all dynamics, both analytically and numerically using random circuits. We find that the third system suppresses teleportation once the spreading message reaches the region of qubits that are entangled with it. In one dimension, both the minimum coupling required for successful teleportation and the fidelity depend on the distance from the injection site to this region, a feature reminiscent of holographic causal shadows. For all-to-all dynamics, successful teleportation is instead restricted to early times and to sufficiently few qubits entangled with the third system. A third system therefore provides spatial, or subsystem, resolution of information spreading that is absent from the two-sided protocol. Our results offer a step toward many-body teleportation networks.

quant-ph↗

arXiv2026

Imaginary time evolution and ground state preparation using unitary multi-copy protocols

Efficient low-energy state preparation is a key objective in quantum computation and quantum simulation. Quantum imaginary-time evolution replaces real-time dynamics with imaginary-time dynamics, exponentially suppressing higher-energy eigenstates. We introduce deterministic unitary protocols that approximate imaginary-time evolution for ground state preparation. The protocols require multiple copies of the system, real-time evolution under the system Hamiltonian, and controlled-SWAP operations (or more general SWAP-generated unitaries). Our analysis focuses on two concrete circuit families: a tree architecture with provable polynomial-in-depth convergence but rapidly growing width, and a compact "hedge" architecture that achieves comparable accuracy with only polynomial width in a heuristic construction supported by numerics. Numerical evidence indicates that mid-circuit post-selection can accelerate convergence with practical success probabilities. Separately, we demonstrate that circuit volume can be traded for the shot complexity of post-circuit observable estimation in the ground state preparation setting. Finally, we outline concrete platform-specific implementations in which multi-copy registers and SWAP-mediated couplings are natural, illustrating how these hybrid analog-digital circuits can complement existing state-preparation methods in the near term.

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arXiv2024

Entanglement spectra from holography

The entanglement spectrum of a bipartite quantum system is given by the distribution of eigenvalues of the modular Hamiltonian. In this work, we compute the entanglement spectrum in the vacuum state for a subregion of a $d$-dimensional conformal field theory (CFT) admitting a holographic dual. In the case of a spherical (or planar) entangling surface, we recover known results in two dimensions, including the Cardy formula in the high energy regime. In higher dimensions $d>2$, we analytically determine a generalization of the Cardy formula valid at large energies and consistent with previous studies of CFT spectra in the literature. We also investigate numerically the spectrum at energy levels far above the modular ground state energy. We extend our analysis to the supersymmetric point of Einstein-Maxwell gravity, providing exact results when $d=2,3$, and a generalization of the Cardy formula at high energies in generic dimension $d$. We consider small shape deformations of a spherical entangling surface, for both the non-supersymmetric and the supersymmetric cases. In all cases we find that the high-energy scaling of the microcanonical entropy with the modular energy is unaffected by the shape deformation. This result suggests that the high-energy regime of the entanglement spectra carries universal information, independent of the shape of the entangling surface.

hep-th↗

arXiv2024

The complexity of entanglement embezzlement

Embezzlement of entanglement is the counterintuitive process in which entanglement is extracted from a resource system using local unitary operations, with almost no detectable change in the resource's state. It has recently been argued that any state of a relativistic quantum field theory can serve as a resource for perfect embezzlement. We study the circuit complexity of embezzlement, using sequences of states that enable arbitrary precision for the process, commonly called universal embezzling families. In addition, we argue that this approach provides a well-defined model for the complexity of embezzlement from quantum field theories. Under fairly general assumptions, we establish a generic lower bound on the complexity, which increases with the precision of the process or embezzled entanglement, and diverges as these become infinite. As an example, we consider a $1d$ critical system as the resource and derive an exponentially growing lower bound on the complexity. Consequently, the findings imply that circuit complexity acts as a physical obstruction to perfect embezzlement. Supplementary to the main results, we derive lower bounds for common models of circuit complexity for state preparation, based on the difference between the Schatten norms of the initial and final states.

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arXiv2023

The Complexity of Being Entangled

Nielsen's approach to quantum state complexity relates the minimal number of quantum gates required to prepare a state to the length of geodesics computed with a certain norm on the manifold of unitary transformations. For a bipartite system, we investigate binding complexity, which corresponds to norms in which gates acting on a single subsystem are free of cost. We reduce the problem to the study of geodesics on the manifold of Schmidt coefficients, equipped with an appropriate metric. Binding complexity is closely related to other quantities such as distributed computing and quantum communication complexity, and has a proposed holographic dual in the context of AdS/CFT. For finite dimensional systems with a Riemannian norm, we find an exact relation between binding complexity and the minimal R\'enyi entropy. We also find analytic results for the most commonly used non-Riemannian norm (the so-called $F_1$ norm) and provide lower bounds for the associated notion of state complexity ubiquitous in quantum computation and holography. We argue that our results are valid for a large class of penalty factors assigned to generators acting across the subsystems. We demonstrate that our results can be borrowed to study the usual complexity (not-binding) for a single spin for the case of the $F_1$ norm which was previously lacking from the literature. Finally, we derive bounds for multi-partite binding complexities and the related (continuous) circuit complexity where the circuit contains at most $2$-local interactions.

hep-th↗

arXiv2022

Energy Transport for Thick Holographic Branes

Universal properties of two-dimensional conformal interfaces are encoded by the flux of energy transmitted and reflected during a scattering process. We develop an innovative method that allows us to use results for the energy transmission in thin-brane holographic models to find the energy transmission for general smooth domain-wall solutions of three-dimensional gravity. Our method is based on treating the continuous geometry as a discrete set of branes. As an application, we compute the transmission coefficient of a Janus interface in terms of its deformation parameter.

hep-th↗

arXiv2021

Entanglement on curved hypersurfaces: A field-discretizer approach

We propose a covariant scheme for measuring entanglement on general hypersurfaces in relativistic quantum field theory. For that, we introduce an auxiliary relativistic field, 'the discretizer', that by locally interacting with the field along a hypersurface, fully swaps the field's and discretizer's states. It is shown, that the discretizer can be used to effectively cut-off the field's infinities, in a covariant fashion, and without having to introduce a spatial lattice. This, in turn, provides us an efficient way to evaluate entanglement between arbitrary regions on any hypersurface. As examples, we study the entanglement between complementary and separated regions in 1+1 dimensions, for flat hypersurfaces in Minkowski space, for curved hypersurfaces in Milne space, and for regions on hypersurfaces approaching null-surfaces. Our results show that the entanglement between regions on arbitrary hypersurfaces in 1+1 dimensions depends only on the space-time endpoints of the regions, and not on the shape of the interior. Our results corroborate and extend previous results for flat hypersurfaces.

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