arXiv subjects

Or Katz

Publications and source records attributed to Or Katz.

At least 37 records · Page 2Linked to original sources

arXiv2024

Observation of string-breaking dynamics in a quantum simulator

Spontaneous particle-pair formation is a fundamental phenomenon in nature. It can, for example, appear when the potential energy between two particles increases with separation, as if they were connected by a tense string. Beyond a critical separation, new particle pairs can form, causing the string to break. String-breaking dynamics in quantum chromodynamics play a vital role in high-energy particle collisions and early universe evolution. Simulating string evolution and hadron formation is, therefore, a grand challenge in modern physics. Quantum simulators, well-suited for studying dynamics, are expected to outperform classical computing methods. However, the required experimental capabilities to simulate string-breaking dynamics have not yet been demonstrated, even for simpler models of the strong force. We experimentally probe, for the first time, the spatiotemporal dynamics of string-breaking in a (1+1)-dimensional $\mathbb{Z}_2$ lattice gauge theory using a fully programmable trapped-ion quantum simulator. We emulate external static charges and strings via site-dependent magnetic-field control enabled by a dual array of tightly focused laser beams targeting individual ions. First, we study how confinement affects isolated charges, finding that they freely spread without string tension but exhibit localized oscillations when tension is increased. Then, we observe and characterize string-breaking dynamics of a string stretched between two static charges after an abrupt increase in string tension. Charge pairs appear near the string edges and spread into the bulk, revealing a route to dynamical string-breaking distinct from the conventional Schwinger mechanism. Our work demonstrates that analog quantum simulators have achieved the necessary control to explore string-breaking dynamics, which may ultimately be relevant to nuclear and high-energy physics.

quant-ph↗

arXiv2024

Optical quantum memory for noble-gas spins based on spin-exchange collisions

Optical quantum memories, which store and preserve the quantum state of photons, rely on a coherent mapping of the photonic state onto matter states that are optically accessible. Here we outline and characterize schemes to map the state of photons onto long-lived but optically-inaccessible collective states of noble-gas spins. The mapping employs coherent spin-exchange interaction arising from random collisions with alkali vapor. We propose efficient storage strategies in two operating regimes and analyze their performance for several proposed experimental configurations.

quant-ph↗

arXiv2024

Observation of the Symmetry-Protected Signature of 3-body Interactions

Identifying and characterizing multi-body interactions in quantum processes remains a significant challenge. This is partly because 2-body interactions can produce an arbitrary time evolution, a fundamental fact often called the universality of 2-local gates in the context of quantum computing. However, when an unknown Hamiltonian respects a U(1) symmetry such as charge or particle number conservation, N-body interactions exhibit a distinct symmetry-protected signature known as the N-body phase, which fewer-body interactions cannot mimic. We develop and demonstrate an efficient technique for the detection of 3-body interactions despite the presence of unknown 2-body interactions. This technique, which takes advantage of GHZ states for phase estimation, requires probing the unitary evolution and measuring its determinant in a small subspace that scales linearly with the system size, making it an efficient approach.

quant-ph↗

arXiv2023

Digital quantum simulation of NMR experiments

Simulations of nuclear magnetic resonance (NMR) experiments can be an important tool for extracting information about molecular structure and optimizing experimental protocols but are often intractable on classical computers for large molecules such as proteins and for protocols such as zero-field NMR. We demonstrate the first quantum simulation of an NMR spectrum, computing the zero-field spectrum of the methyl group of acetonitrile using four qubits of a trapped-ion quantum computer. We reduce the sampling cost of the quantum simulation by an order of magnitude using compressed sensing techniques. We show how the intrinsic decoherence of NMR systems may enable the zero-field simulation of classically hard molecules on relatively near-term quantum hardware and discuss how the experimentally demonstrated quantum algorithm can be used to efficiently simulate scientifically and technologically relevant solid-state NMR experiments on more mature devices. Our work opens a practical application for quantum computation.

quant-ph↗

arXiv2023

Observation of a finite-energy phase transition in a one-dimensional quantum simulator

One of the most striking many-body phenomena in nature is the sudden change of macroscopic properties as the temperature or energy reaches a critical value. Such equilibrium transitions have been predicted and observed in two and three spatial dimensions, but have long been thought not to exist in one-dimensional (1D) systems. Fifty years ago, Dyson and Thouless pointed out that a phase transition in 1D can occur in the presence of long-range interactions, but an experimental realization has so far not been achieved due to the requirement to both prepare equilibrium states and realize sufficiently long-range interactions. Here we report on the first experimental demonstration of a finite-energy phase transition in 1D. We use the simple observation that finite-energy states can be prepared by time-evolving product initial states and letting them thermalize under the dynamics of a many-body Hamiltonian. By preparing initial states with different energies in a 1D trapped-ion quantum simulator, we study the finite-energy phase diagram of a long-range interacting quantum system. We observe a ferromagnetic equilibrium phase transition as well as a crossover from a low-energy polarized paramagnet to a high-energy unpolarized paramagnet in a system of up to $23$ spins, in excellent agreement with numerical simulations. Our work demonstrates the ability of quantum simulators to realize and study previously inaccessible phases at finite energy density.

quant-ph↗

arXiv2023

Observation of trap-assisted formation of atom-ion bound states

Pairs of free particles cannot form bound states in elastic collision due to momentum and energy conservation. In many ultracold experiments, however, the particles collide in the presence of an external trapping potential which can couple the center-of-mass and relative motions and assist the formation of bound-states. Here, we report on observation of weakly bound molecular states formed between one ultracold $^{87}$Rb atom and a single trapped $^{88}$Sr$^+$ ion in the presence of a linear Paul trap. We show that bound states can form efficiently in binary collisions, and enhance the rate of inelastic processes. By observing electronic spin-exchange rate, we study the dependence of these bound states on the collision energy and magnetic field and extract the average molecular binding energy $E_{\textrm{bind}}=0.7(1)$ mK$\cdot k_B$ and the mean lifetime of the molecule $τ=0.5(1)\,μ$s, with good agreement with molecular-dynamics simulations. Our simulations predict a highly unusual power-law distribution of molecular lifetimes with a mean that is dominated by extreme, long-lived, events. The dependence of the molecular properties on the trapping parameters opens new avenues to study and control ultracold collisions.

physics.atom-ph↗

arXiv2022

Continuous Symmetry Breaking in a Trapped-Ion Spin Chain

One-dimensional systems exhibiting a continuous symmetry can host quantum phases of matter with true long-range order only in the presence of sufficiently long-range interactions. In most physical systems, however, the interactions are short-ranged, hindering the emergence of such phases in one dimension. Here we use a one-dimensional trapped-ion quantum simulator to prepare states with long-range spin order that extends over the system size of up to $23$ spins and is characteristic of the continuous symmetry-breaking phase of matter. Our preparation relies on simultaneous control over an array of tightly focused individual-addressing laser beams, generating long-range spin-spin interactions. We also observe a disordered phase with frustrated correlations. We further study the phases at different ranges of interaction and the out-of-equilibrium response to symmetry-breaking perturbations. This work opens an avenue to study new quantum phases and out-of-equilibrium dynamics in low-dimensional systems.

quant-ph↗

arXiv2022

Experimental Implementation of an Efficient Test of Quantumness

A test of quantumness is a protocol where a classical user issues challenges to a quantum device to determine if it exhibits non-classical behavior, under certain cryptographic assumptions. Recent attempts to implement such tests on current quantum computers rely on either interactive challenges with efficient verification, or non-interactive challenges with inefficient (exponential time) verification. In this paper, we execute an efficient non-interactive test of quantumness on an ion-trap quantum computer. Our results significantly exceed the bound for a classical device's success.

quant-ph↗

arXiv2022

Demonstration of three- and four-body interactions between trapped-ion spins

Quantum processors use the native interactions between effective spins to simulate Hamiltonians or execute quantum gates. In most processors, the native interactions are pairwise, limiting the efficiency of controlling entanglement between many qubits. Here we experimentally demonstrate a new class of native interactions between trapped-ion qubits, extending conventional pairwise interactions to higher order. We realize three- and four-body spin interactions as examples, showing that high-order spin polynomials may serve as a new toolbox for quantum information applications.

quant-ph↗

arXiv2022

$N$-body interactions between trapped ion qubits via spin-dependent squeezing

We describe a simple protocol for the single-step generation of $N$-body entangling interactions between trapped atomic ion qubits. We show that qubit state-dependent squeezing operations and displacement forces on the collective atomic motion can generate full $N$-body interactions. Similar to the Mølmer-Sørensen two-body Ising interaction at the core of most trapped ion quantum computers and simulators, the proposed operation is relatively insensitive to the state of motion. We show how this $N$-body gate operation allows the single-step implementation of a family of $N$-bit gate operations such as the powerful $N$-Toffoli gate, which flips a single qubit if and only if all other $N$-$1$ qubits are in a particular state.

quant-ph↗

arXiv2022

Programmable quantum simulations of bosonic systems with trapped ions

Trapped atomic ion crystals are a leading platform for quantum simulations of spin systems, with programmable and long-range spin-spin interactions mediated by excitations of phonons in the crystal. We describe a complementary approach for quantum simulations of bosonic systems using phonons in trapped-ion crystals, here mediated by excitations of the trapped ion spins. The scheme features a high degree of programability over a dense graph of bosonic couplings and is suitable for hard problems such as boson sampling and simulations of long range bosonic and spin-boson Hamiltonians.

quant-ph↗

arXiv2022

Programmable N-body interactions with trapped ions

Trapped atomic ion qubits or effective spins are a powerful quantum platform for quantum computation and simulation, featuring densely connected and efficiently programmable interactions between the spins. While native interactions between trapped ion spins are typically pairwise, many quantum algorithms and quantum spin models naturally feature couplings between triplets, quartets or higher orders of spins. Here we formulate and analyze a mechanism that extends the standard Mølmer-Sørensen pairwise entangling gate and generates a controllable and programmable coupling between $N$ spins of trapped ions. We show that spin-dependent optical forces applied at twice the motional frequency generate a coordinate-transformation of the collective ion motion in phase-space, rendering displacement forces that are nonlinear in the spin operators. We formulate a simple framework that enables a systematic and faithful construction of high-order spin Hamiltonians and gates, including the effect of multiple modes of motion, and characterize the performance of such operations under realistic conditions.

quant-ph↗

arXiv2022

Interactive Protocols for Classically-Verifiable Quantum Advantage

Achieving quantum computational advantage requires solving a classically intractable problem on a quantum device. Natural proposals rely upon the intrinsic hardness of classically simulating quantum mechanics; however, verifying the output is itself classically intractable. On the other hand, certain quantum algorithms (e.g. prime factorization via Shor's algorithm) are efficiently verifiable, but require more resources than what is available on near-term devices. One way to bridge the gap between verifiability and implementation is to use "interactions" between a prover and a verifier. By leveraging cryptographic functions, such protocols enable the classical verifier to enforce consistency in a quantum prover's responses across multiple rounds of interaction. In this work, we demonstrate the first implementation of an interactive quantum advantage protocol, using an ion trap quantum computer. We execute two complementary protocols -- one based upon the learning with errors problem and another where the cryptographic construction implements a computational Bell test. To perform multiple rounds of interaction, we implement mid-circuit measurements on a subset of trapped ion qubits, with subsequent coherent evolution. For both protocols, the performance exceeds the asymptotic bound for classical behavior; maintaining this fidelity at scale would conclusively demonstrate verifiable quantum advantage.

quant-ph↗

arXiv2022

Strong coupling of alkali spins to noble-gas spins with hour-long coherence time

Nuclear spins of noble gases can maintain coherence for hours at ambient conditions owing to their extraordinary isolation by the enclosing, complete electronic shells. This isolation, however, impedes the ability to manipulate and control them by optical means or by physical coupling to other spin gases. Here we experimentally achieve strong coherent coupling between noble-gas spins and the optically-accessible spins of alkali-metal vapor. Stochastic spin-exchange collisions, underlying the coupling, accumulate to a coherent periodic exchange of spin excitations between the two gases. We obtain a coupling rate 10 times higher than the decay rate, observe the resultant avoided crossing in the spectral response of the spins, and demonstrate the external control over the coupling by magnetic fields. These results open a route for efficient and rapid interfacing with noble-gas spins for applications in quantum sensing and information.

quant-ph↗

arXiv2022

NASDUCK: New Constraints on Axion-like Dark Matter from Floquet Quantum Detector

We report on the first results of the Noble and Alkali Spin Detectors for Ultralight Coherent darK matter (NASDUCK) collaboration. We search for the interactions of Axion-Like Particles (ALPs) with atomic spins using an earth-based precision quantum detector as it traverses through the galactic dark matter halo. The detector is composed of spin-polarized xenon gas which can coherently interact with a background ALP dark matter field and an in-situ rubidium Floquet optical-magnetometer. Conducting a five months-long search, we derive new constraints on ALP-proton and ALP-neutron interactions in the $4\times 10^{-15}-4\times 10^{-12}{~\rm eV/c^2}$ mass range. Our limits on the ALP-proton (ALP-neutron) couplings improve upon previous terrestrial bounds by up to 3 orders of magnitude for masses above $4\times 10^{-14}{~\rm eV/c^2}$ ($4\times 10^{-13}{~\rm eV/c^2}$). Moreover, barring the uncertain supernova constraints, the ALP-proton bound improves on all existing terrestrial and astrophysical limits, partially closing the unexplored region for couplings in the range $10^{-6}~{\rm GeV^{-1}}$ to $2\times 10^{-5}~{\rm GeV^{-1}}$. Finally, we also cast bounds on pseudo-scalar dark matter models in which dark matter is quadratically-coupled to the nucleons.

hep-ph↗

arXiv2022

Enhanced coupling of electron and nuclear spins by quantum tunneling resonances

Noble-gas spins feature hours long coherence times owing to their great isolation from the environment, and find practical usage in various applications. However, this isolation leads to extremely slow preparation times, relying on weak spin transfer from an electron-spin ensemble. Here we propose a controllable mechanism to enhance this transfer rate. We analyze the spin dynamics of helium-3 atoms with hot, optically-excited potassium atoms and reveal the formation of quasi-bound states in resonant binary collisions. We find a resonant enhancement of the spin-exchange cross section by up to six orders of magnitude and two orders of magnitude enhancement for the thermally averaged, polarization rate-coefficient. We further examine the effect for various other noble gases and find that the enhancement is universal. We outline feasible conditions under which the enhancement may be experimentally observed and practically utilized.

quant-ph↗

arXiv2021

Critical dynamics and phase transition of a strongly interacting warm spin-gas

Phase transitions are emergent phenomena where microscopic interactions drive a disordered system into a collectively ordered phase. Near the boundary between two phases, the system can exhibit critical, scale-invariant behavior. Here, we report on a second-order phase transition accompanied by critical behavior in a system of warm cesium spins driven by linearly-polarized light. The ordered phase exhibits macroscopic magnetization when the interactions between the spins become dominant. We measure the phase diagram of the system and observe the collective behavior near the phase boundaries, including power-law dependence of the magnetization and divergence of the susceptibility. Out of equilibrium, we observe a critical slow-down of the spin response time by two orders of magnitude, exceeding five seconds near the phase boundary. This work establishes a controlled platform for investigating equilibrium and nonequilibrium properties of magnetic phases.

quant-ph↗

arXiv2021

Quantum-Logic Detection of Chemical Reactions

Studies of chemical reactions by a single pair of atoms in a well defined quantum state constitute a corner stone in quantum chemistry. Yet, the number of demonstrated techniques which enable observation and control of a single chemical reaction is handful. Here we propose and demonstrate a new technique to study chemical reactions between an ultracold neutral atom and a cold ion using quantum logic. We experimentally study the release of hyperfine energy in a reaction between an ultracold rubidium atom and isotopes of singly ionized strontium for which we do not have experimental control. We detect the reaction outcome and measure the reaction rate of the chemistry ion by reading the motional state of a logic ion via quantum logic, in a single shot. Our work opens new avenues and extends the toolbox of studying chemical reactions, with existing experimental tools, for all atomic and molecular ions in which direct laser cooling and state detection are unavailable.

physics.atom-ph↗