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Quantum circuits interact with the environment via several temperature-dependent degrees of freedom. Multiple experiments to-date have shown that most properties of superconducting devices appear to plateau out at T ≈ 50 mK – far above the refrigerator base temperature. This is for example reflected in the thermal state population of qubits, in excess numbers of quasiparticles, and polarisation of surface spins – factors contributing to reduced coherence. We demonstrate how to remove this thermal constraint by operating a circuit immersed in liquid 3He. This allows to efficiently cool the decohering environment of a superconducting resonator, and we see a continuous change in measured physical quantities down to previously unexplored sub-mK temperatures. The 3He acts as a heat sink which increases the energy relaxation rate of the quantum bath coupled to the circuit a thousand times, yet the suppressed bath does not introduce additional circuit losses or noise. Such quantum bath suppression can reduce decoherence in quantum circuits and opens a route for both thermal and coherence management in quantum processors. Removing excess energy (cooling) and reducing noise in superconducting quantum circuits is central to improved coherence. Lucas et al. demonstrate cooling of a superconducting resonator and its noisy environment to sub-mK temperatures by immersion in liquid 3He. [ABSTRACT FROM AUTHOR]

Recent experiments have indicated surface spins in superconducting devices to be associated with both flux- and charge noise. In particular, for superconducting resonators, where the frequency noise is dominated by the electric field from the resonator coupling to spurious two-level material defects, information on noise in applied magnetic fields is lacking. Here, we present measurements of frequency noise in a superconducting resonator with a centre frequency f 0 = 6.1 GHz in fields exceeding the Zeeman splitting of surface spins (up to 310 mT), showing that the charge-induced noise is unaffected by the applied magnetic field. [ABSTRACT FROM AUTHOR]

Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of twolevel systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices. [ABSTRACT FROM AUTHOR]

Slow noise processes, with characteristic timescales ~1 s, have been studied in planar superconducting resonators. A frequency-locked loop is employed to track deviations of the resonator center frequency with high precision and bandwidth. Comparative measurements are made in varying microwave drive and temperature, and between bare resonators and those with an additional dielectric layer. All resonators are found to exhibit flicker frequency noise which increases with decreasing microwave drive. We also show that an increase in temperature results in a saturation of flicker noise in resonators with an additional dielectric layer, while bare resonators stop exhibiting flicker noise, instead showing a random frequency walk process. [ABSTRACT FROM AUTHOR]