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arXiv:1905.12532 · PRX Quantum

Quantum Interface for Noble-Gas Spins Based on Spin-Exchange Collisions

Or Katz, Roy Shaham, Ofer Firstenberg

Published Jan 10, 2022• 38 citations
arXivHTMLPDF

Abstract

An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment.This isolation, however, is a mixed blessing, limiting the ability of these ensembles to interface with other quantum systems coherently.Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times.We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly couples the macroscopic quantum states of the two spin ensembles.Despite their stochastic and random nature, weak collisions enable entanglement and reversible exchange of nonclassical excitations in an efficient, controllable, and deterministic process.With recent experiments now entering the strong-coupling regime, this interface paves the way toward realizing hour-long quantum memories and entanglement at room temperature.

DOI
10.1103/prxquantum.3.010305

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An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment.This isolation, however, is a mixed blessing, limiting the ability of these ensembles to interface with other quantum systems coherently.Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times.We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly couples the macroscopic quantum states of the two spin ensembles.Despite their stochastic and random nature, weak collisions enable entanglement and reversible exchange of nonclassical excitations in an efficient, controllable, and deterministic process.With recent experiments now entering the strong-coupling regime, this interface paves the way toward realizing hour-long quantum memories and entanglement at room temperature.
An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment. This isolation, however, is a mixed blessing, limiting the ability of these ensembles to coherently interface with other quantum systems. Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times. We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly couples the macroscopic quantum states of the two spin ensembles. Despite their stochastic and random nature, weak collisions enable entanglement and reversible exchange of nonclassical excitations in an efficient, controllable, and deterministic process. We outline feasible parameters for reaching the strong-coupling regime, paving the way towards an experimental realization of hour-long quantum memories and entanglement at room-temperature.
Nuclear spins of noble-gas atoms are exceptionally isolated from the environment and can maintain their quantum properties for hours at room temperature. Here we develop a mechanism for entangling two such distant macroscopic ensembles by using coherent light input. The interaction between the light and the noble-gas spins in each ensemble is mediated by spin-exchange collisions with alkali-metal spins, which are only virtually excited. The relevant conditions for experimental realizations with ^{3}He or ^{129}Xe are outlined.
Isolation from environment leads to the days-long lifetime of noble-gas nuclear spins, but also brings great challenges to the preparation, manipulation, and measurement of nuclear-spin quantum states. Here we find that nuclear spin squeezing, with ultra-long lifetime and huge atomic number, can be efficiently obtained and manipulated based on the coherent spin-exchange interaction between alkali-metal and noble-gas ensembles. Thanks to the considerable advantage of our proposal in preparing the spin squeezing of the macroscopic atomic ensemble with a huge atomic number, even the nuclear spin-squeezed state containing 10^20 atoms or more is obtainable with preexisting techniques. Further, the days-long storage and measurement of nuclear spin squeezing can be performed by the coherent manipulation of a magnetic field. This proposal can be implemented in hot atomic ensembles, whose ease of access and high adaptability to various environments will significantly facilitate the research and application of nuclear-spin nonclassical states in precision measurement, quantum information, and fundamental physics.
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 quasibound states in resonant binary collisions. We find a resonant enhancement of the spin-exchange cross section by up to 6 orders of magnitude and 2 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.
Nuclear spins of noble gases exhibit exceptionally long coherence times and can potentially serve as a long-lived storage medium for quantum information. We analyze and compare the performance of two mechanisms for mapping the quantum state of light onto the collective spin state of noble gases. The first mechanism utilizes collisional exchange with the electronic spin state of metastable noble-gas atoms, while the second relies on spin-exchange collisions with ground-state alkali-metal atoms. We describe the operation of an optical quantum memory relying on these two mechanisms using a compact model and study strategies that optimize the memory storage efficiency. Through numerical simulations, we identify optimal sequences for storing optical signals with different signal bandwidths and electronic spin relaxation rates. This work highlights the qualitative difference between the two approaches for using noble gases as long-lived quantum memories at noncryogenic conditions and outlines the regimes in which they are expected to be efficient.
Light storage, the controlled and reversible mapping of photons onto long-lived states of matter, enables memory capability in optical quantum networks. Prominent storage media are warm alkali vapors due to their strong optical coupling and long-lived spin states. In a dense gas, the random atomic collisions dominate the lifetime of the spin coherence, limiting the storage time to a few milliseconds. Here we present and experimentally demonstrate a storage scheme that is insensitive to spin-exchange collisions, thus enabling long storage times at high atomic densities. This unique property is achieved by mapping the light field onto spin orientation within a decoherence-free subspace of spin states. We report on a record storage time of 1 s in room-temperature cesium vapor, a 100-fold improvement over existing storage schemes. Furthermore, our scheme lays the foundations for hour-long quantum memories using rare-gas nuclear spins.