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.
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.
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.
We demonstrate a circuit QED analog of an atomic micromaser that utilizes an artificial, multi level atom, pumped into a population-inverted state by a microwave tone, as the gain medium. Our demonstration is enabled by the flexibility of the circuit QED platform, which allowed us to precisely engineer the level-structure, coupling, and dissipation of the micromaser components. Our device shows rich physics and perhaps points to ways to use the recent developments in the domain of microwave quantum circuits to probe the domain of maser physics.
Superconducting microwave circuits are a ubiquitous and important tool for devices that exploit the phenomena of superconductivity and cryogenic temperatures as an environment for achieving the generation, manipulation, and detection of quantum states - required for the ongoing development of quantum technologies. In particular, superconducting circuits are a promising platform for the universal quantum computer, which will require an unprecedented density of quantum-coherent elements to perform large-scale quantum-enhanced calculations and simulations, using the framework of cavity quantum lectrodynamics.Dissipation and heat in these superconducting circuits is a key source of error and inefficiency, however the thermodynamics in this regime is poorly understood despite its increasing relevancy.This thesis describes the integration of superconducting resonators and artificial atoms derived from superconducting quantum circuits with ultra-sensitive bolometry, for looking at heat transport through superconducting circuits. We will describe the physics and operation of each of these elements, before combining and utilising them to perform heat transport measurements through a superconducting artificial atom coupled to two resonators, each terminated by a normal-metal mesoscopic resistor, with the resistor temperature measured and temperature gradients across the circuit induced by superconducting tunnel-probes. We will present tunable heat transport through this system, firstly when the resonators are symmetric, allowing us to observe the role of dissipation-limited coupling of the resonators to the artificial atom on the locality of the heat transport, then on an asymmetric system, demonstrating a directional rectification of the heat transport. Additionally, we will discuss how each element of the system can be individually characterised, in particular the quality factor of superconducting resonators in the highly-dissipative limit, by exploiting the superconducting transition to perform a background reference. It is suggested that this hybrid quantum system, and these initial experiments provide a promising platform in the emergent field of circuit quantum thermodynamics. We believe that the techniques and tools developed during this thesis present key steps towards the understanding of the thermodynamics of quantum circuits, towards the realisation of devices that can explore heat transport in the quantum limit, such as a quantum heat engine.
We report an experimental realization of a three-terminal photonic heat transport device based on a superconducting quantum circuit. The central element of the device is a flux qubit made of a superconducting loop containing three Josephson junctions, which can be tuned by magnetic flux. It is connected to three resonators terminated by resistors. By heating one of the resistors and monitoring the temperatures of the other two, we determine photonic heat currents in the system and demonstrate their tunability by magnetic field at the level of 1 aW. We determine system parameters by performing microwave transmission measurements on a separate nominally identical sample and, in this way, demonstrate clear correlation between the level splitting of the qubit and the heat currents flowing through it. Our experiment is an important step towards realization of heat transistors, heat amplifiers, masers pumped by heat and other quantum heat transport devices.
The exceptionally strong coupling realizable between superconducting qubits and photons stored in an on-chip microwave resonator allows for the detailed study of matter–light interactions in the realm of circuit quantum electrodynamics (QED). Here we investigate the resonant interaction between a single transmon-type multilevel artificial atom and weak thermal and coherent fields. We explore up to three photon dressed states of the coupled system in a linear response heterodyne transmission measurement. The results are in good quantitative agreement with a generalized Jaynes–Cummings model. Our data indicate that the role of thermal fields in resonant cavity QED can be studied in detail using superconducting circuits.
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.