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arXiv:2010.04975 · Physical Review A

Single-atom maser with an engineered circuit for population inversion

А. Соколова, Gleb Fedorov, Evgeni V. Il’ichev, O. V. Astafiev

Published Jan 14, 2021• 10 citations
arXivHTMLPDF

Abstract

We present a blueprint for a maser with a single three-level transmon superconducting artificial atom. The system can be pumped coherently via a two-photon process, and to achieve high population inversion, the relaxation rate of the metastable state is increased via an auxiliary low-$Q$ cavity coupled to a transition between the transmon excited states. We show numerically that such a maser can operate both in the intermediate-coupling regime with super-Poissonian photon statistics and in the strong-coupling regime, where the statistics is sub-Poissonian. For the former the maser exhibits thresholdless behavior, and for the latter there is a well-defined pumping threshold. A useful side effect of the auxiliary resonator is that it allows to overcome the photon blockade effect for the pump, which would otherwise prevent a high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.

DOI
10.1103/physreva.103.013718

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We present a blueprint for a maser with a single three-level transmon superconducting artificial atom. The system can be pumped coherently via a two-photon process, and to achieve high population inversion, the relaxation rate of the metastable state is increased via an auxiliary low-QQQ cavity coupled to a transition between the transmon excited states. We show numerically that such a maser can operate both in the intermediate-coupling regime with super-Poissonian photon statistics and in the strong-coupling regime, where the statistics is sub-Poissonian. For the former the maser exhibits thresholdless behavior, and for the latter there is a well-defined pumping threshold. A useful side effect of the auxiliary resonator is that it allows to overcome the photon blockade effect for the pump, which would otherwise prevent a high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.
Reaching high cavity population with a coherent pump in the strong-coupling regime of a single-atom laser is impossible due to the photon blockade effect. In this work, we experimentally demonstrate that in a single-atom maser based on a transmon strongly coupled to two resonators it is possible to pump over a dozen of photons into the system. The first high-quality resonator plays a role of usual lasing cavity, and the second one presents a controlled dissipation channel, bolstering population inversion, and modifies the energy level structure to lift the blockade. As a confirmation of lasing action, we observe conventional laser features such as the narrowing of emission linewidth and external signal amplification. Additionally, we report unique single-atom features: self-quenching and several lasing thresholds.
We present a theoretical model of an on-chip three-level maser in a superconducting circuit based on a single artificial atom and pumped by a temperature gradient between thermal baths coupled to different interlevel transitions. We show that maser powers of the order of a few femtowatts, well exceeding the resolution of the sensitive bolometry, can be achieved with typical circuit parameters. We also demonstrate that population inversion in the artificial atom can be detected without measuring coherent radiation output of the maser. For that purpose, the system should operate as a three-terminal heat transport device. The hallmark of population inversion is the influx of heat power into the weakly coupled output terminal even though its temperature exceeds the temperatures of the two other terminals. The proposed method of on-chip conversion of heat into microwave radiation and control of energy-level populations by heating provide additional useful tools for circuit quantum electrodynamics experiments.
Lasing - an effect of orthodox quantum mechanics - was discovered in 1955 and recognized by the Nobel Prize in 1964 due to its fundamentality. Nowadays, lasers and masers routinely work with electromagnetic waves and consist of a resonator with an active medium - usually a system of atoms with population inversion mechanism. Amazingly, quantum mechanics remains valid even when electromagnetic waves are replaced by vibrations of a crystal lattice, and, therefore, photons by phonons, even though are not fundamental particles. By implementing acoustic resonators coupled to an atom with a mechanism of population inversion, the lasing effect in sound can be achieved. In this paper, we demonstrate the single artificial atom SASER (Sound Amplification by Stimulated Emission of Radiation) action by utilizing a surface acoustic wave (SAW) resonator on quartz coupled to a deliberately designed superconducting three-level quantum system (artificial atom), in which population inversion is realized. The SASER operates in the ultrasound range at a frequency about 3 GHz. Acoustic-to-electric signals are converted via piezo-electric effect and the circuit elements; an artificial atom and input/outputs are coupled via the acoustic waves. We observe amplification of the waves and their strong self-emission with a significant narrowing of the linewidth. The phonon number generated in the system exceeds 90.
We present the quantum theory of a microscopic maser operating on a degenerate two-photon transition between levels of the same parity. We derive both a master equation and a Fokker-Planck equation for this system, and show that quantum effects may have a substantial influence on the behavior of the maser. They modify the oscillation threshold and make external triggering of this maser unnecessary, whereas, according to semiclassical theory, such a triggering is required to start up the maser oscillation. We derive the phase-diffusion properties of the field and show that the diffusion coefficient is complex in this case, its imaginary part being associated with a frequency shift of the field inside the cavity. We show that, in steady state, the photon-number statistics is sub-Poissonian for a wide range of pumping rates.
The possibility of maser action using a current-biased mesoscopic Josephson junction in a high-Q microcavity is discussed. A mesoscopic Josephson junction behaves like an artificial atom as far as the interaction with the photon field is concerned. Under a certain bias current, the Josephson ``atom'' is resonantly excited or pumped by quantum-mechanical fluctuations of the Josephson phase, i.e., macroscopic resonant tunneling. When the pumping overcomes the loss of photons from the cavity, maser action is possible. Quantum statistical properties of photons are also investigated numerically, taking into acount the microcavity effect on the basis of a Jaynes-Cummings model with pumping and cavity damping. We found that a mesoscopic Josephson junction within the high-Q microcavity acts as a thresholdless maser with sub-Poissonian photon statstics. \textcopyright{} 1996 The American Physical Society.