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Register a new userThermometry and memcapacitance with qubit-resonator system
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Added by
Sergey Shevchenko N.
Publication date
2018
fields
Physics
and research's language is
English
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We study theoretically dynamics of a driven-dissipative qubit-resonator system. Specifically, a transmon qubit is coupled to a transmission-line resonator; this system is considered to be probed via a resonator, by means of either continuous or pulsed measurements. Analytical results obtained in the semiclassical approximation are compared with calculations in the semi-quantum theory as well as with the previous experiments. We demonstrate that the temperature dependence of the resonator frequency shift can be used for the system thermometry and that the dynamics, displaying pinched-hysteretic curve, can be useful for realization of memory devices, the quantum memcapacitors.
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Superconducting qubits acting as artificial two-level atoms allow for controlled variation of the symmetry properties which govern the selection rules for single and multiphoton excitation. We spectroscopically analyze a superconducting qubit-resonator system in the strong coupling regime under one- and two-photon driving. Our results provide clear experimental evidence for the controlled transition from an operating point governed by dipolar selection rules to a regime where one- and two-photon excitations of the artificial atom coexist. We find that the vacuum coupling between qubit and resonator can be straightforwardly extracted from the two-photon spectra where the detuned two-photon drive does not populate the relevant resonator mode significantly.
We study the dynamics of a qubit-resonator system, when the resonator is driven by two signals. The interaction of the qubit with the high-amplitude driving we consider in terms of the qubit dressed states. Interaction of the dressed qubit with the second probing signal can essentially change the amplitude of this signal. We calculate the transmission amplitude of the probe signal through the resonator as a function of the qubits energy and the driving frequency detuning. The regions of increase and attenuation of the transmitted signal are calculated and demonstrated graphically. We present the influence of the signal parameters on the value of the amplification, and discuss the values of the qubit-resonator system parameters for an optimal amplification and attenuation of the weak probe signal.
Diamond-based microelectromechanical systems (MEMS) enable direct coupling between the quantum states of nitrogen-vacancy (NV) centers and the phonon modes of a mechanical resonator. One example, diamond high-overtone bulk acoustic resonators (HBARs), feature an integrated piezoelectric transducer and support high-quality factor resonance modes into the GHz frequency range. The acoustic modes allow mechanical manipulation of deeply embedded NV centers with long spin and orbital coherence times. Unfortunately, the spin-phonon coupling rate is limited by the large resonator size, $>100~mu$m, and thus strongly-coupled NV electron-phonon interactions remain out of reach in current diamond BAR devices. Here, we report the design and fabrication of a semi-confocal HBAR (SCHBAR) device on diamond (silicon carbide) with $fcdot Q>10^{12}$($>10^{13}$). The semi-confocal geometry confines the phonon mode laterally below 10~$mu$m. This drastic reduction in modal volume enhances defect center electron-phonon coupling. For the native NV centers inside the diamond device, we demonstrate mechanically driven spin transitions and show a high strain-driving efficiency with a Rabi frequency of $(2pi)2.19(14)$~MHz/V$_{p}$, which is comparable to a typical microwave antenna at the same microwave power.
We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87 %; of the missing 13 %, only 3 % is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.
Long-distance two-qubit coupling, mediated by a superconducting resonator, is a leading paradigm for performing entangling operations in a quantum computer based on spins in semiconducting materials. Here, we demonstrate a novel, controllable spin-photon coupling based on a longitudinal interaction between a spin qubit and a resonator. We show that coupling a singlet-triplet qubit to a high-impedance superconducting resonator can produce the desired longitudinal coupling when the qubit is driven near the resonators frequency. We measure the energy splitting of the qubit as a function of the drive amplitude and frequency of a microwave signal applied near the resonator antinode, revealing pronounced effects close to the resonator frequency due to longitudinal coupling. By tuning the amplitude of the drive, we reach a regime with longitudinal coupling exceeding $1$ MHz. This demonstrates a new mechanism for qubit-resonator coupling, and represents a stepping stone towards producing high-fidelity two-qubit gates mediated by a superconducting resonator.
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