# Coherently refreshed acoustic phonons for extended light storage

## TL;DR

This paper introduces a resonant optical reinforcement scheme that extends the lifetime of acoustic phonons in waveguides, enabling on-chip optical storage up to 40 ns and potentially up to microseconds, surpassing previous limitations.

## Contribution

The authors demonstrate a novel method to counteract intrinsic acoustic decay using synchronized optical pulses, significantly extending phonon-based light storage times.

## Key findings

- Achieved 40 ns on-chip optical storage, four times the intrinsic phonon lifetime.
- Confirmed coherence of stored signals via homodyne detection after 40 ns.
- Theoretically possible to reach storage times up to microseconds with GHz bandwidth.

## Abstract

Acoustic waves can serve as memory for optical information, however, acoustic phonons in the GHz regime decay on the nanosecond timescale. Usually this is dominated by intrinsic acoustic loss due to inelastic scattering of the acoustic waves and thermal phonons. Here we show a way to counteract the intrinsic acoustic decay of the phonons in a waveguide by resonantly reinforcing the acoustic wave via synchronized optical pulses. This scheme overcomes the previous constraints of phonon-based optical signal processing for light storage and memory. We experimentally demonstrate on-chip storage up to 40 ns, four times the intrinsic acoustic lifetime in the waveguide. We confirm the coherence of the scheme by detecting the phase of the delayed optical signal after 40 ns using homodyne detection. Through theoretical considerations we anticipate that this concept allows for storage times up to microseconds within realistic experimental limitations while maintaining a GHz bandwidth of the optical signal. The refreshed phonon-based light storage removes the usual bandwidth-delay product limitations of e.g. slow-light schemes.