Schrodinger's catapult: Launching multiphoton quantum states from a microwave cavity memory

TL;DR

This paper demonstrates a fast, efficient method to convert complex multiphoton quantum states from a microwave cavity into traveling signals, enabling advanced quantum network functionalities.

Contribution

It introduces a controlled, high-efficiency conversion technique for multiphoton quantum states from a cavity to propagating modes using Josephson junction nonlinearity.

Findings

Conversion time ~500 ns, much faster than cavity lifetime

Conversion efficiency exceeds 90%

Ability to generate entanglement via partial conversion

Abstract

Encoding quantum states in complex multiphoton fields can overcome loss during signal transmission in a quantum network. Transmitting quantum information encoded in this way requires that locally stored states can be converted to propagating fields. Here we experimentally show the controlled conversion of multiphoton quantum states, like "Schr\"odinger cat" states, from a microwave cavity quantum memory into propagating modes. By parametric conversion using the nonlinearity of a single Josephson junction, we can release the cavity state in ~500 ns, about 3 orders of magnitude faster than its intrinsic lifetime. This `catapult' faithfully converts arbitrary cavity fields to traveling signals with an estimated efficiency of > 90%, enabling on-demand generation of complex itinerant quantum states. Importantly, the release process can be controlled precisely on fast time scales, allowing us to generate entanglement between the cavity and the traveling mode by partial conversion. Our system can serve as the backbone of a microwave quantum network, paving the way towards error-correctable distribution of quantum information and the transfer of highly non-classical states to hybrid quantum systems.