IQIM Postdoctoral and Graduate Student Seminar

Note: this is a special IQIM seminar beginning at 3 pm on May 3.

Abstract: Single-photon detection, challenging to realize in the microwave domain, is an essential component in many quantum optics experiments. In this talk I describe a quantum non-demolition (QND) detector for propagating microwave photons and characterize its performance using a single-photon source. To this aim, we implemented a cavity-assisted conditional phase gate between an incident photon and a superconducting three-level system. By reading out the state of the qutrit with single shot resolution, we reach an external (internal) photon-detection fidelity of 50% (71%) [1]. By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate the QND character of the detector. Similarly, we realize a single-shot QND parity detector for multi-photon propagating microwave fields. By exploiting the measurement back-action on an incident coherent field we herald propagating cat states of the radiation field with average fidelity of 90 % [2]. In the same setup, we combine parity measurements with a real-time displacement operations to perform complete Wigner tomography of propagating fields. We also demonstrate a mode reduction technique which enables parity measurements of the number of photons encoded in multiple time bins. We expect multi-photon QND measurements of itinerant fields to develop into an important tool for the creation of future quantum communication networks in the microwave domain.

[1] J.-C. Besse et al., Phys. Rev. X 8, 021003 (2018)

[2] J.-C. Besse et al., Quantum Device Lab (2019)

This research was performed in a collaboration between Jean-Claude Besse, Simone Gasparinetti, Michele C. Collodo, Theo Walter, Philipp Kurpiers, Marek Pechal, Ants Remm, Jonas Krause, Christopher Eichler, and Andreas Wallraff