Room Temperature Quantum Optics
| Noble-gas isotopes with non-zero nuclear spin, such as helium-3, feature day-long spin lifetimes and hours-long coherence times, at or above room temperature. They are prominent in various fields, from precision sensing and medical imaging to searches for new physics, and they hold promise for future quantum information applications such as optical quantum memories and the generation of long-lived entanglement. The latter rely on the feasibility of preparing the collective spin state of the gas and controlling its quantum excitations.
Polarized ensembles of alkali-metal spins or noble-gas spins can carry such collective excitations, corresponding classically to a tilt of the collective spin about the polarization axis. These can be modelled as quantum excitations of a harmonic oscillator. Remarkably, the quantum description persists even for gaseous ensembles undergoing rapid diffusion and for overlapping ensembles that interact via atomic collisions. The collective state of alkali-metal spins can be addressed and coherently controlled by optical means. The same, however, cannot be done for the nuclear spins of noble gases, which lack any optical transition from the ground levels. Instead, one can access the noble-gas spins by collisions with another spin gas such as alkali-metal vapour which possess an optically accessible spin. |
 Ultra-long coherent spin gas at room temperature. a. In a glass cell containing optically alkali-metal spins (red) and noble-gas spins (blue), the alkali spins can be manipulated optically, and the polarized ensembles couple via stochastic atomic collisions, which accumulate to a collective and spin-exchange interaction at a rate J. This enables the deterministic transfer of quantum spin excitations between the two spin gases. b. Precession of the helium-3 (noble-gas) spins, measured with low spin polarizations and normalized to the initial value, features a coherence time of about 2 hours, holding great promise for quantum applications at ambient conditions. See Nature Physics, 18 506-510 (2022).
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 Light can be stopped. When photons (shown as purple wave-packets) interact with alkali-metal atoms, and another control beam (depicted in red) is present, the atoms absorb the photons and encode their quantum information onto their many-body spin state. This process effectively slows down the photons to almost zero velocity. The relatively-long lifetime of these encoded states allows them to be used as memory for hundreds of milliseconds at room temperature, as evidenced by measured signals at different storage durations. See Nature Communications 9 2074 (2018) for details.
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The interface with alkali-metal spins therefore paves the way towards wider applications of noble-gas spins in quantum optics for long-distance entanglement at ambient conditions, as well as to fundamental research of the limits of quantum theory for entangled macroscopic objects. Another particularly intriguing prospect is extending the lifetime of quantum memories for photons via mapping to noble-gas spins. Currently, quantum memories for light use only alkali-metal spins (see image to left), mapping the state of a photon onto the collective alkali-metal spin state. However, owing to relaxation mechanisms of the alkali-metal spins that have a single valence electron, their lifetime is typically limited to hundreds of milliseconds. Coupling to noble gas spins could extend this lifetime towards hours long.
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Selected Publications
- “Light storage for one second in room-temperature alkali vapor“. Katz, Firstenberg. Nature Communications 9 2074 (2018).
- “Long-Lived Entanglement Generation of Nuclear Spins Using Coherent Light“. Katz, Shaham, Polzik, Firstenberg. Phys. Rev. Lett. 124 043602 (2020).
- “Strong coupling of alkali-metal spins to noble-gas spins with an hour-long coherence time”. Shaham, Katz, Firstenberg. Nature Physics, 18 506-510 (2022).