Counting statistics of ultra-broadband microwave photons

TL;DR

This paper presents measurements of counting statistics for broadband microwave photons, demonstrating the generation of entanglement and quantum steering using a tunnel junction as a source, over a wide frequency range.

Contribution

It introduces a method to analyze photon statistics of broadband microwave signals and demonstrates broadband squeezing and entanglement generation with a tunnel junction.

Findings

Achieved ultra-wide squeezing spectrum up to 0.9 billion entangled bits/sec

Observed quantum steering in microwave photons

Showed broadband squeezing implies entanglement between modes

Abstract

We report measurements of counting statistics, average and variance, of microwave photons of ill-defined frequency : bichromatic photons, i.e. photons involving two well separated frequencies, and "white" broadband photons. Our setup allows for the analysis of single photonic modes of arbitrary waveform over the 1-10 GHz frequency range. The photon statistics are obtained by on-the-fly numerical calculation from the sampled time-dependent voltage. Using an ac+dc biased tunnel junction as a source of quantum microwave, we report an ultra-wide squeezing spectrum representing a competitive source for entanglement generation (up to 0.9 billion measured entangled bits per second) easily achievable experimentally. We also report the observation of quantum steering by the tunnel junction, and show how the presence of squeezing of a broadband mode implies the existence of entanglement between two modes it encompasses.