Full-Wave Modeling of the Emission of Single Photon Sources

The development of efficient and deterministic single photon sources remains a challenge for implementing scalable quantum information processing systems. In addition to having high efficiency, one of the most sought after properties of singe photon sources is for them to produce highly indistinguishable photons. This is required so that photons produced by different sources can coherently interfere with each other, producing the uniquely quantum effects that are necessary for many quantum processing algorithms to be effective. A number of studies have looked at the fundamental bounds on the indistinguishability of single photons produced by various hardware platforms. However, these studies neglect the loss of indistinguishability that can occur due to manufacturing tolerances and different photon propagation environments experienced by photons produced by different sources.

To provide a more complete description of the indistinguishability a single photon source can achieve in a practical geometry, we have developed a full-wave modeling process to more rigorously compute the spatial and temporal dependence of the emission of a single photon source. This allows us to more completely account for the specific layout of a single photon source and the electromagnetic propagation environment the photon is emitted into. Our approach is generally applicable to microwave or optical frequency single photon sources. We have begun testing this numerical modeling approach by analyzing a microwave single photon source that consists of a transmon qubit embedded in a coplanar waveguide cavity resonator. Our model has shown promising results that match expectations for device performance based on the experimental results achieved for a similarly designed device.

(a) Device layout of a microwave frequency single photon source with zoomed in views showing the current density (arrows) and charge density (color) at key parts of the design computed using a custom-developed computational electromagnetics method that is suitable for performing extremely broadband simulations of multiscale devices. (b) Wide bandwidth time delay analysis of signals received near the ``top'' and ``bottom'' of the output capacitor show undesirable slotline propagation modes are generated. (c) Normalized spectra of the effective current source formed by the transmon qubit found using open quantum system modeling techniques.

Expectation of the photon number operator in the dominant slotline mode for different Rabi pulse areas to excite the transmon to various initial states.