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 Schr\"odinger 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.
Highlights
The parity P of a wave function ψ governs whether a system has an even or odd number of excitations n
We experimentally demonstrate that this process creates heralded, propagating, even- or odd-parity cat states when conditioned on the single-shot parity measurement outcome
We further explore the nonclassical properties of the generated cat states for mean photon numbers of up to n 1⁄4 2 by extracting the normalized zero-time second-order correlation function gð2Þð0Þ 1⁄4 ha†2a2i=ha†ai2
Summary
The parity P of a wave function ψ governs whether a system has an even or odd number of excitations n. For example, the parity of the number of photons stored in a microwave cavity is determined either by direct measurements [3], providing immediate access to the value of P, or indirect measurements [4], requiring the reconstruction of P from another measured quantity. Direct measurements of the parity are frequently used to reconstruct quantum states of radiation fields stored in microwave cavities [3,5,6]. Parity measurements of propagating quantum radiation fields, which can be used as the carriers of information in quantum networks, have recently been realized in the optical domain [7] with neutral-atom-based systems [8],. Parity measurements have been demonstrated, for example, with superconducting qubits for measurement-based entanglement generation [13], for elements of error correction [14,15,16], and entanglement stabilization [17], an experiment which was performed with ions [18,19]
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