Quantum state correction using a measurement-based feedforward mechanism

Abstract

One of the weaknesses of quantum optical state postselection schemes is the low success probability. Typically there is a trade-off between amplifier properties such as success probability and output state fidelity. However, here we present a state comparison amplifier for optical coherent states, which features an active measurement and feedforward mechanism to correct for errors made during the initial amplification. The simple and relatively low latency mechanism allows us to correct for a binary phase alphabet. We demonstrate a significant simultaneous improvement in the amplifier characteristic parameters: output state fidelity, correct state fraction, and success probability. This demonstrates that nondeterministic quantum amplification can be enhanced significantly by measurement and feedforward.

Number-state reconstruction with a single SPAD

“…Single-photon avalanche detectors (SPADs) are critical for many areas of research in atomic physics, quantum optics, and quantum communication as well as a variety of other fields. [1][2][3][4][5][6] When a single photon impinges on a SPAD, a detectable "avalanche" of current results; a quenching circuit turns off the avalanche after some time. 7,8 Importantly, during the avalanche, additional photons may arrive, but the noise on the avalanche is so large that additional excitations are unresolvable.…”

Ghost displacement

“…This effect has been exploited to amplify coherent states with high gain. [16][17][18][19][20] Here we apply this type of technique to a thermal state. The coherent state measurement conditionally reduces the thermal component of the output state and adds a coherent component.…”

Parity-swap state comparison amplifier for Schrödinger cat states

“…Here we introduce an optical amplifier for Schrödinger cat states that works without requiring prior knowledge of the input state, that relies on Gaussian resources, beamsplitters and Geiger mode detectors and offers a reasonably high gain and high output quality for a range of low ampli-tude cat states. The proposed scheme is inspired by the so called state comparison amplifier (SCAMP) [26][27][28][29][30][31] a non-deterministic amplifier that has been shown to achieve high gain and high output quality for discrete sets of input coherent states of light.…”