Key Findings
The University of Illinois Urbana-Champaign (UIUC) team has demonstrated an integrated nanophotonic chip that stores up to 20 separate photons simultaneously with storage times reaching 1.2 microseconds. The device preserved the quantum character of the light with a measured fidelity lower bound of 96.6%. Notably, the chip is built on a thin-film lithium niobate (TFLN) platform, a material already used in wafer-scale commercial photonics manufacturing for fiber-optic telecommunications.
Technical Details
The device employs an atomic frequency comb (AFC) combined with spectral hole burning to delay photons. The waveguide, approximately 0.6 mm long, is doped with erbium atoms. A tuned laser creates a comb-shaped absorption pattern; the spacing of the comb’s teeth determines the storage time. To stabilize spectral holes and suppress thermal noise, the chip operates at 30 millikelvin within a 1.5-tesla magnetic field.
- Multiplexing: Supports 20 temporal modes across an acceptance bandwidth of 2.2 GHz.
- Fidelity: Confirmed via time-bin qubits with fringe visibility of 96.6 ± 1.9%.
- Noise: Remained below 0.2 photons per retrieved photon.
- Efficiency: Internal retrieval efficiency was 2.9% for a 300-nanosecond delay and 0.7% at one microsecond.
Background & Context
Quantum networking requires the ability to pause photons to synchronize probabilistic operations between processors and repeaters. Traditional optical delay lines are impractical for microsecond delays; a 1-microsecond delay would require roughly 150 meters of photonic wire, leading to extreme signal attenuation. The UIUC approach avoids this by transferring the quantum state into erbium atoms rather than relying on geometric length.
Significance & Outlook
The one-microsecond threshold is critical as it matches the round-trip light-travel time for signals in large data centers or campus-scale networks. This capability is essential for high-speed links, such as the photonic link recently demonstrated by IonQ, which requires memory to buffer entangled states while classical confirmation signals travel between nodes. Because the TFLN platform is already known to commercial foundries, this technology can be scaled without requiring specialized quantum optics expertise at the manufacturing level.
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