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2021 International Applied Computational Electromagnetics Society Symposium (ACES)

Full- Wave Modeling of the Emission of a Microwave Frequency Single Photon Source

Thomas E. Roth, Weng Cho Chew

Published Aug 1, 2021• 2 citations
Publisher

Abstract

Single photon sources are an important component in many quantum information processing systems. Despite their importance, current modeling methods predominantly focus on developing optimistic performance bounds, and are not conducive to performing engineering optimization studies. To enhance the capability of modeling methods, we propose a process to utilize the classical electromagnetic dyadic Green's function of a system as an integral component of determining the emitted photon states produced by a single photon source. Importantly, the Green's function can be readily computed using standard fullwave numerical methods, making it a viable analysis tool. We demonstrate this process by characterizing the emission of a microwave frequency single photon source that uses a transmon as a quantum emitter, and find qualitative agreement with a fabricated device that has similar design characteristics.

DOI
10.1109/aces53325.2021.00090

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Single photon sources are an important component in many quantum information processing systems. Despite their importance, current modeling methods predominantly focus on developing optimistic performance bounds, and are not conducive to performing engineering optimization studies. To enhance the capability of modeling methods, we propose a process to utilize the classical electromagnetic dyadic Green's function of a system as an integral component of determining the emitted photon states produced by a single photon source. Importantly, the Green's function can be readily computed using standard fullwave numerical methods, making it a viable analysis tool. We demonstrate this process by characterizing the emission of a microwave frequency single photon source that uses a transmon as a quantum emitter, and find qualitative agreement with a fabricated device that has similar design characteristics.
Understanding the spontaneous emission rate of transmon qubits is an important step in the design of many quantum electromagnetic devices, such as single photon sources and quantum computers. Despite its importance, the spontaneous emission rate is often determined using approximate circuit models or is inferred from measurements on a fabricated device. To improve the accuracy of predictions, it is better to use full-wave numerical methods for this problem. In this work, we show how this can be done with a recently developed field-based description of transmon qubits coupled to an electromagnetic environment. We demonstrate this process by computing the spontaneous emission rate of a single photon source and find qualitative agreement with a similar fabricated device.
The spontaneous emission rate (SER) is an important figure of merit for any quantum bit (qubit), as it can play a significant role in the control and decoherence of the qubit. As a result, accurately characterizing the SER for practical devices is an important step in the design of quantum information processing devices. Here, we specifically focus on the experimentally popular platform of a transmon qubit, which is a kind of superconducting circuit qubit. Despite the importance of understanding the SER of these qubits, it is often determined using approximate circuit models or is inferred from measurements on a fabricated device. To improve the accuracy of predictions in the design process, it is better to use full-wave numerical methods that can make a minimal number of approximations in the description of practical systems. In this work, we show how this can be done with a recently developed field-based description of transmon qubits coupled to an electromagnetic environment. We validate our model by computing the SER for devices similar to those found in the literature that have been well-characterized experimentally. We further cross-validate our results by comparing them to simplified lumped element circuit and transmission line models as appropriate.
In this work, we present a numerical framework for modeling single photon emission from a two level system in open and dissipative systems beyond the Markovian approximation. The method can be readily integrated into standard computational electromagnetic (CEM) solvers such as finite difference time domain (FDTD) and finite element method (FEM). We numerically verify the completeness of boundary and medium assisted modes in the modified Langevin noise formalism by reconstructing the imaginary part of the dyadic Greens function through modal expansion in three dimensions. This reconstruction enables a first principles description of atom field interaction via the multi mode Jaynes Cummings model in open and dissipative environments. Within the single excitation manifold, we show that the memory kernel of a two level system is determined by the imaginary part of the Greens function, implying that radiative modes alone govern the relevant dynamics. The proposed framework thus provides a Greens function based approach for describing atomic population and single photon dynamics, directly compatible with Maxwell solvers. We then present concrete strategies for implementing our method in both FDTD and FEM frameworks, demonstrating its practical applicability. We further verify numerical results for a lossy Lorentz Drude type mirror, including both the case of a TLS near a finite sized metallic mirror and that of a TLS centered in a Fabry Perot cavity. This work establishes a rigorous foundation for incorporating quantum emitter dynamics into computational electromagnetics, thereby extending classical solvers toward quantum light matter interactions.
Abstract We present a detailed study of a microwave single-photon source utilizing a transmon qubit asymmetrically coupled to two transmission lines: a weakly coupled drive line and a strongly coupled emission line. Our design allows for the generation of single photons in the microwave regime, which are essential for quantum communication, computing, and sensing applications. In addition to single-photon generation, the same design functions as a power sensor and enables precise measurement of the system’s attenuation. This dual functionality allows us to calibrate the noise of our amplification chain. This enables a self-calibrated architecture in which the same device acts simultaneously as the photon source and as a reference standard, eliminating the need for external tones or calibrated inputs. With this calibration we reconstruct the density matrix of the emitted photon state, for which we achieve a fidelity of 61.4% and measure a second-order correlation function of g ( 2 ) ( 0 ) = 0.06 − 0.06 + 0.45 , indicating quantum nature and single-photon characteristics. These results confirm generation of single photons and demonstrate the potential of transmon qubits in advancing quantum technologies in the microwave domain.
This work presents a full-wave Green's function framework for modeling collective and coherent single-photon emission from multiple quantum emitters embedded in complex electromagnetic structures. Starting from a transverse modal completeness relation of modified Langevin noise formalism, we derive a closed set of coupled equations for population dynamics and frequency-resolved field amplitudes in the single-excitation regime. Since the electromagnetic reservoir is not traced out at the level of the dynamical amplitudes, the emitted single-photon dynamics can be modeled within the same closed set of equations without Markovian approximation in open and dissipative environments. We demonstrate that finite-bandwidth truncation of the spectral density leads to systematic deviations in coherent dispersive interactions, even when dissipative rates appear converged. To restore causal consistency, we introduce a counter-term compensation scheme that restores the missing dispersive contributions without modifying the retained non-Markovian memory kernel. To validate the scheme and demonstrate the practicality of the proposed framework, we present numerical examples ranging from benchmark configurations to a three-dimensional dispersive ring-resonator structure via finite element method. These capabilities provide a practical route for rigorously incorporating full-wave electromagnetic simulations into non-Markovian multi-emitter quantum electrodynamics, enabling predictive modeling of collective emission, coherent energy exchange, and single-photon radiation in realistic open structures.
Abstract We demonstrate an on-demand source of microwave single photons with 71–99% intrinsic quantum efficiency. The source is narrowband (300 kHz) and tuneable over a 600 MHz range around 5.2 GHz. Such a device is an important element in numerous quantum technologies and applications. The device consists of a superconducting transmon qubit coupled to the open end of a transmission line. A π-pulse excites the qubit, which subsequently rapidly emits a single photon into the transmission line. A cancellation pulse then suppresses the reflected π-pulse by 33.5 dB, resulting in 0.005 photons leaking into the photon emission channel. We verify strong antibunching of the emitted photon field and determine its Wigner function. Non-radiative decay and 1/f flux noise both affect the quantum efficiency. We also study the device stability over time and identify uncorrelated discrete jumps of the pure dephasing rate at different qubit frequencies on a time scale of hours, which we attribute to independent two-level system defects in the device dielectrics, dispersively coupled to the qubit. Our single-photon source with only one input port is more compact and scalable compared to standard implementations.