Parity Detection of Propagating Microwave Fields

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 a decay of an excitation has occurred, information which 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 n 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. * jbesse@phys.ethz.ch † Current address: Quantum Technology Laboratory, Chalmers University of Technology, SE-412 96 Gteborg, Sweden qubits for measurement based entanglement generation [13], for elements of error correction [14][15][16], and entanglement stabilization [17], an experiment which was also performed with ions [18,19].

Energetics of a Single Qubit Gate

“…While surprising when considering the average experiment, it is well explained by a weak-value model. Looking forward, it would be interesting to perform a full quantum tomography of the drive state using newly-developed itinerant mode detectors [36,37] by first displacing the quantum state towards low photon numbers. From a thermodynamic point of view, this measurement backaction on the energy could be used to build new thermodynamic engines that are powered by measurement [38][39][40][41][42][43][44][45][46][47][48][49][50].…”

Loss-tolerant concatenated Bell-state measurement with encoded coherent-state qubits for long-range quantum communication

“…Regarding the direct measurement, parity measurements in cavities have been demonstrated and realized via Rydberg atom interacting with photons [78], Ramsey interferometry [39,79], or strong nonlinear Hamiltonian of a Josephson circuit [36]. However, parity measurements of propagating waves have not been covered much yet except a few studies such as parity measurement via strong nonlinear optical switching devices [80,81] or a cavity QED system realized in superconducting circuits [82]. Indirect measurement, or photon-number-resolving (PNR) detection, is a more actively studied topic due to its wide availability [83].…”

A flying Schrödinger cat in multipartite entangled states

“…Preparing Schrödinger cat states have attracted wide research interest from testing quantum foundations to demonstrating the increasing controllability of modern quantum systems. Over the decades, Schrödinger cat states have been successfully prepared in various physical systems, including vibrational states of a trapped ion [3], propagating photon modes [4][5][6][7][8][9][10][11] and microwave photons confined in superconducting cavities coupled with either Rydberg atoms [12,13] or superconducting qubits [14]. By entangling with more continuousvariable modes, a multipartite Schrödinger's cat can be obtained as N (|α ⊗n ± |−α ⊗n ), where |α represents a coherent state, N is a normalization factor, and n represents the number of photonic modes, essentially describing quantum entanglement of coherent states [15].…”