Abstract
The parity of the number of elementary excitations present in a quantum system provides important insights into its physical properties. Parity measurements are used, for example, to tomographically reconstruct quantum states or to determine if the decay of an excitation has occurred, information that can be used for quantum error correction in computation or communication protocols. Here, we demonstrate a versatile parity detector for propagating microwaves, which distinguishes between radiation fields containing an even or odd number of photons, both in a single-shot measurement and without perturbing the parity of the detected field. We showcase applications of the detector for direct Wigner tomography of propagating microwaves and heralded generation of Schrödinger cat states. This parity detection scheme is applicable over a broad frequency range and may prove useful, for example, for heralded or fault-tolerant quantum communication protocols.
1 More- Received 26 September 2019
- Accepted 24 January 2020
DOI:https://doi.org/10.1103/PhysRevX.10.011046
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Knowing whether a quantum system has an even or odd number of particles can provide useful intelligence about the system. Such “parity” measurements can allow researchers to reconstruct quantum states or determine whether or not a decay has occurred—information that can be used for quantum error correction. Here, we report the first experiment capable of determining whether a propagating microwave pulse contains an even or odd number of photons.
The quantum nondemolition nature of our approach and the high fidelity achieved allow us to observe alternating parity as we add single photons to a propagating pulse. We also use the access to parity information to reveal the presence of Schrödinger cat states—quantum superpositions of two distinct classical states—with fundamentally different statistical properties from a classical itinerant input: strongly bunched even states and antibunched odd states. These demonstrations go substantially beyond what has been achieved with optical photons. Our scheme also realizes a crucial and hitherto missing component for detecting photon loss in quantum networks based on parity changes.
This method is applicable over a broad frequency range and therefore holds the promise to become a versatile tool for identifying errors in quantum transmission channels. In this respect, it might provide an important ingredient in future fault-tolerant quantum networks.