Experimental noiseless linear amplification using weak measurements

TL;DR

This paper demonstrates a novel approach to noiseless quantum signal amplification by applying weak measurements and quantum logic gates, preserving coherence and enabling longer-distance quantum communication.

Contribution

It introduces an experimental method combining weak measurements with heralded amplification, advancing quantum communication techniques.

Findings

Achieved controlled amplification gain based on measurement strength.

Preserved quantum coherence during the amplification process.

Validated the approach using interferometric coherence measurements.

Abstract

The viability of quantum communication schemes rely on sending quantum states of light over long distances. However, transmission loss can degrade the signal strength, adding noise. Heralded noiseless amplification of a quantum signal can provide a solution by enabling longer direct transmission distances and by enabling entanglement distillation. The central idea of heralded noiseless amplification---a conditional modification of the probability distribution over photon number of an optical quantum state---is suggestive of a parallel with weak measurement: in a weak measurement, learning partial information about an observable leads to a conditional back-action of a commensurate size. Here we experimentally investigate the application of weak, or variable-strength, measurements to the task of heralded amplification, by using a quantum logic gate to weakly couple a small single-optical-mode quantum state (the signal) to an ancilla photon (the meter). The weak measurement is carried out by choosing the measurement basis of the meter photon and, by conditioning on the meter outcomes, the signal is amplified. We characterise the gain of the amplifier as a function of the measurement strength, and use interferometric methods to show that the operation preserves the coherence of the signal.