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Entanglement and quantum information

Can sound waves carry entangled quantum states across a chip?

Zivari A, Fiaschi N, Burgwal R, et al. · Science advances · 2022

Open access · cc by · source: Europe PMC

Single quanta of sound travelling along a tiny silicon waveguide were shown to carry entanglement, passing a Bell test with a partner photon.

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Study at a glance

Design
Other — Single silicon optomechanical cavity coupled to a phononic waveguide, driven by write/read laser pulses at 10 mK with single-photon detection.
N
One device; more than 500 coincidence events for the entanglement witness, about 30 events per hour for the Bell test.
Population
A silicon optomechanical cavity attached to a roughly 100-micrometre phononic waveguide
Outcome
Photon cross-correlations, entanglement witness R, and CHSH parameter S

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

The phonon round-trip time in the waveguide was 126 ns and packets lasted about 30 ns, so early and late phonons were distinguishable. An entanglement witness gave R = 0.72 ± 0.06, below the classical threshold of 1. A CHSH Bell test between the photon and the travelling phonon qubit gave S = 2.32 ± 0.08, exceeding the classical limit of 2 by about 4 standard deviations.

Methodology

The team built a silicon nanobeam cavity that couples light and mechanical vibration, attached to a waveguide whose free end reflects phonons back. Cooled to 10 mK, the device was hit with weak blue-detuned write pulses that create photon-phonon pairs and red-detuned read pulses that convert phonons back to photons. Two write pulses half a round trip apart plus an interferometer made an early/late (time-bin) phonon qubit, whose correlations with photons were measured on single-photon detectors.

Limitations

The mechanical lifetime is short, so in this device phonons could only travel a few millimetres; longer distances are projected, not shown. Event rates were very low, so the Bell dataset took 56 hours, and heating from optical absorption limited fidelity. Only two time bins in one device were demonstrated, and entanglement was not distributed between two separate points or to other qubit types.

How this study connects

Role on claims

Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.

  • SupportsQuantum entanglementconcept

    Sound waves can carry quantum information on chip.

    Entanglement can be verified inside a chip with non-photonic carriers: a photon entangled with a travelling phonon qubit gave a CHSH value S = 2.32 ± 0.08, above the classical bound of 2.

    Evidence for the claim as stated.

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