We report an experimental demonstration of resonance fluorescence in a two-level superconducting artificial atom under two driving fields coupled to a detuned cavity. One of the fieldsis classical and the other is varied from quantum (vacuum fluctuations) to classical one by controlling the photon number inside the cavity. The device consists of a transmon qubit strongly coupled to a one-dimensional transmission line and a coplanar waveguide resonator. We observe a sideband anti-crossing and asymmetry in the emission spectra of the system through a one-dimensional transmission line, which is fundamentally different from the weak coupling case. By changing the photon number inside the cavity, the emission spectrum of our doubly driven system approaches to the case when the atom is driven by two classical bichromatic fields. We also measure the dynamical evolution of the system through the transmission line and study the properties of the first-order correlation function, Rabi oscillations and energy relaxation in the system. The study of resonance fluorescence from an atom driven by two fields promotes understanding decoherence in superconducting quantum circuits and may find applications in superconducting quantum computing and quantum networks.
An electromagnetic wave propagating through a waveguide with a strongly coupled superconducting artificial two-level atom exhibits an evolving superposition with the atom. The Rabioscillations in the atom result from a single excitation-relaxation, corresponding to photon absorption and stimulated emission from/to the field. In this study, we investigate the time-dependent behavior of the transmitted field and extract its spectra. The scattered fields are described using input-output theory. We demonstrate that the time evolution of the propagating fields, due to interaction, encapsulates all information about the atom. Additionally, we deduce the dynamics of the incoherent radiation component from the measured first-order correlation function of the field.
We demonstrate non-equilibrium steady-state photon transport through a chain of five coupled artificial atoms simulating the driven-dissipative Bose-Hubbard model. Using transmissionspectroscopy, we show that the system retains many-particle coherence despite being coupled strongly to two open spaces. We show that system energy bands may be visualized with high contrast using cross-Kerr interaction. For vanishing disorder, we observe the transition of the system from the linear to the nonlinear regime of photon blockade in excellent agreement with the input-output theory. Finally, we show how controllable disorder introduced to the system suppresses this non-local photon transmission. We argue that proposed architecture may be applied to analog simulation of many-body Floquet dynamics with even larger arrays of artificial atoms paving an alternative way to demonstration of quantum supremacy
(Martin Leib: The topic of this article is a central theme of my entire work and yet the authors managed to ignore everything I have worked on …)
We present a blueprint for a maser with a single three-level artificial atom. The artificial atom is a superconducting quantum system of a transmon layout coupled to two resonators.The system is pumped via a two-photon process. To achieve a population inversion, we engineer the quantum system and optimize its parameters, particularly the relaxation via an auxiliary low-Q cavity coupled to a transition between two 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. An interesting side-effect of the auxiliary resonator is that it allows overcoming the photon blockage effect for the pump, which would otherwise prohibit reaching high photon population. Finally, we observe the bistability of the steady-state Wigner function and the self-quenching effect for some parameters.
In this work, we irradiate a superconducting artificial molecule composed of two magnetic-flux-tunable transmons with microwave light while monitoring its state via joint dispersivereadout. At certain fluxes, the molecule demonstrates a complex spectrum deviating qualitatively from the solution of the Schrödinger equation without driving. We reproduce the observed extra spectral lines accurately by numerical simulations, and find them to be a consequence of an Autler-Townes-like effect when a single tone is simultaneously dressing the system and probing the transitions between new eigenstates. We present self-consistent analytical models accounting both these processes at the same time that agree well with both experiment and numerical simulation. This study is an important step towards understanding the behaviour of complex systems of many atoms interacting coherently with strong radiation.
Single-photon sources are of great interest because they are key elements in different promising applications of quantum technologies. Here we demonstrate a highly efficient tunableon-demand microwave single-photon source based on a transmon qubit with the intrinsic emission efficiency more than 99%. To confirm the single-photon property of the source, we study the single-photon interference in a Hanbury-Brown-Twiss (HBT) type setup and measure the correlation functions of the emission field using linear detectors with a GPU-enhanced signal processing technique. The antibunching in the second-order correlation function is clearly observed. The theoretical calculations agree well with the experimental results. Such a high-quality single-photon source can be used as a building block of devices for quantum communication, simulations and information processing in the microwave regime.
We study four- and higher-order wave mixing of continuous coherent waves on a single superconducting artificial atom. Narrow side peaks of different orders of nonlinearity resultingfrom elastic multi-photon scattering on the atom are observed and investigated. We derive an analytical expression for the peak amplitudes and show that the ratio of any two adjacent peaks is a function of driving amplitudes and detuning. This is attributed to the photon distribution in the coherent states and provides a measure for characterisation of photon statistics in non-classical coherent waves. We also demonstrate an Autler-Townes-like splitting of side peaks, the magnitude of which scales with the scattering order.
The quantum regime in acoustic systems is a focus of recent fundamental research in the new field of Quantum Acoustodynamics (QAD). Systems based on surface acoustic waves having anadvantage of easy integration in two-dimensions are particularly promising for the demonstration of novel effects in QAD and development of novel devices of quantum acousto-electronics. We demonstrate the vacuum mode of the surface acoustic wave resonator by coupling it to a superconducting artificial atom. The artificial atom is implemented into the resonator formed by two Brag mirrors. The results are consistent with expectations supported by the system model and our calculations. This work opens the way to map analogues of quantum optical effects into acoustic systems.
We report development and microwave characterization of rf SQUID (Superconducting QUantum Interference Device) qubits, consisting of an aluminium-based Josephson junction embedded ina superconducting loop patterned from a thin film of TiN with high kinetic inductance. Here we demonstrate that the systems can offer small physical size, high anharmonicity, and small scatter of device parameters. The hybrid devices can be utilized as tools to shed further light onto the origin of film dissipation and decoherence in phase-slip nanowire qubits, patterned entirely from disordered superconducting films.
We demonstrate coherent dynamics of quantized magnetic fluxes in a superconducting loop with a weak link – a nanobridge patterned from the same thin NbN film as the loop. Thebridge is a short rounded shape constriction, close to 10 nm long and 20 – 30 nm wide, having minimal width at its center. Quantum state control and coherent oscillations in the driven time evolution of the tunnel-junctionless system are achieved. Decoherence and energy relaxation in the system are studied using a combination of microwave spectroscopy and direct time-domain techniques. The effective flux noise behavior suggests inductance fluctuations as a possible cause of the decoherence.