Optical time-domain quantum state tomography on a subcycle scale

TL;DR

This paper introduces a method to perform full quantum state tomography of broadband electromagnetic fields in the time domain using electro-optic sampling, enabling subcycle resolution of quantum states.

Contribution

It develops a theoretical framework linking electro-optic sampling measurements to quantum state phase-space distributions, advancing quantum tomography techniques.

Findings

Relates photon-count probabilities to phase-space quasiprobability distributions.

Identifies thermalization noise due to entanglement breaking in ultrabroadband sampling.

Proposes mitigation strategies for noise to enable broadband quantum state reconstruction.

Abstract

Following recent progress in the experimental application of electro-optic sampling to the detection of the quantum fluctuations of the electromagnetic-field ground state and ultrabroadband squeezed states on a subcycle scale, we propose an approach to elevate broadband electro-optic sampling from a spectroscopic method to a full quantum tomography scheme, able to reconstruct a broadband quantum state directly in the time-domain. By combining two recently developed methods to theoretically describe quantum electro-optic sampling, we analytically relate the photon-count probability distribution of the electro-optic signal to a transformed phase-space quasiprobability distribution of the sampled quantum state as a function of the time delay between the sampled mid-infrared pulsed state and an ultrabroadband near-infrared pump/probe pulse. We catalog and analyze sources of noise and show that in quantum electro-optic sampling with an ultrabroadband pump pulse one can expect to observe thermalization due to entanglement breaking. Mitigation of the thermalization noise enables a tomographic reconstruction of broadband quantum states while granting access to its dynamics on a subcycle scale.