Abstract
We study quantum state tomography, entanglement detection and channel noise reconstruction of propagating quantum microwaves via dual-path methods. The presented schemes make use of the following key elements: propagation channels, beam splitters, linear amplifiers and field quadrature detectors. Remarkably, our methods are tolerant to the ubiquitous noise added to the signals by phase-insensitive microwave amplifiers. Furthermore, we analyse our techniques with numerical examples and experimental data, and compare them with the scheme developed in Eichler et al (2011 Phys. Rev. Lett. 106 220503; 2011 Phys. Rev. Lett. 107 113601), based on a single path. Our methods provide key toolbox components that may pave the way towards quantum microwave teleportation and communication protocols.
Highlights
In circuit quantum electrodynamics [1, 2], a superconducting qubit is coupled to the quantized modes of the electromagnetic field in a superconducting microwave resonator
Since the typical operating frequency of the system ranges between 1 and 10 GHz, and since the output signal of the resonator can propagate along transmission lines, it is of key importance to study how to measure propagating quantum microwave signals and how to use them to perform quantum information processing (QIP) protocols [3]
Our numerical simulations show that the dual-path method (DPM) performs better than the SPM introduced in [19, 20] at the cost of some experimental resources: an additional beam splitter and an additional amplifying channel
Summary
In circuit quantum electrodynamics (cQED) [1, 2], a superconducting qubit is coupled to the quantized modes of the electromagnetic field in a superconducting microwave resonator. The first experimental result of quantum state tomography in the microwave regime is reported by Menzel et al [12] It is based on a technique called the dual-path method (DPM), and was inspired by earlier consideration of Mariantoni et al [13]. The JPA allows, in principle, to measure a single quadrature without adding noise Since this method is conceptually very different from our moment-based approach, we choose to compare our method to the single-path, or reference state, method (SPM) implemented in [19, 20], which reconstruct the moments of the input signal by using only a single path with a previous tomography of the amplifier noise.
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