Attosecond Access to the Quantum Noise of Light

TL;DR

This paper demonstrates that attosecond streaking can directly measure the quantum noise and phase properties of intense light fields on sub-cycle timescales, enabling quantum-optical metrology in the strong-field regime.

Contribution

It introduces a phase-sensitive method using attosecond streaking to characterize quantum states of light, including coherent and squeezed states, through delay-resolved photoelectron spectra.

Findings

First moment of photoelectron distribution reveals coherent displacement.

Second moment captures quantum noise fluctuations and phase modulation.

Simulations confirm the ability to retrieve phase and squeezing information.

Abstract

Characterizing the quantum state of intense light fields on sub-cycle timescales remains beyond the reach of existing methods. Here, we show that attosecond streaking provides direct, phase-sensitive access to the quantum properties of the driving field through delay-resolved photoelectron spectra. Using a Feynman--Vernon treatment, we decompose the influence of the quantized driving field on the photoelectron into coherent and fluctuation contributions. This yields a simple, moment-based characterization of the light state: the first moment of the photoelectron momentum distribution reveals the coherent displacement, while the second central moment captures the fluctuation contribution and, for squeezed states, exhibits a clear modulation at twice the driving frequency, directly signaling phase-sensitive quantum noise. Time-dependent Schr\"odinger equation simulations confirm these relations and enable retrieval of the coherent phase, the squeezing phase, and the relative strengths of the coherent and fluctuation contributions from delay-resolved spectra. Taken together, these results establish attosecond streaking as a route to sub-cycle quantum-optical metrology in the strong-field regime.