We propose a mechanism to interface a transmission line resonator (TLR) with a nanomechanical resonator (NAMR) by commonly coupling them to a charge qubit, a Cooper-pair box with a controllable gate voltage. Integrated in this quantum transducer or simple quantum network, the charge qubit plays the role of a controllable quantum node coherently exchanging quantum information between the TLR and NAMR. With such an interface, a quasiclassical state of the NAMR can be created by controlling a single-mode classical current in the TLR. Alternatively, a “Cooper pair” coherent output through the transmission line can be driven by a single-mode classical oscillation of the NAMR.

In principle, gravitational waves could exist at any frequency. Recently, the LIGO-Virgo Collaboration detected gravitational waves (GWs) by probing their mechanical responses with laser interferometers. The detected GWs are in the intermediate-frequency band, i.e., GW150914: 35–250 Hz; GW151226: 35–450 Hz; GW170104: 30–350 Hz; GW170814: 35–450 Hz; and GW170817: 30–350 Hz. Alternatively, in this paper we investigate the observable electromagnetic responses (EMRs) of the GWs, passing through an alternating magnetic field. We show that, differing from the original Gertsenshtein-Zeldovich effect (which is the second-order effect of the amplitude of the GW passing through a high stationary magnetic field and consequently is too weak to be detected), the EMRs of the GWs in the present configuration are the first-order perturbation effects and thus the induced perturbation photon fluxes are detectable with the current well-developed weak-light detection techniques. Furthermore, we show that the wave impedances of the GW-induced electromagnetic wave perturbations are very different from those of the background electromagnetic noises (i.e., $\cong 377\mathrm{\Omega }$ for EM radiation in the background flat space-time). Therefore, with a properly designed wave-matching technique, the stronger background EM noise (without any GW information) can be effectively filtered out, and thus only the GW-induced perturbation photon fluxes are conducted to the detectors. The configuration proposed here could be utilized to actively look for GWs in a sufficiently wide frequency band, depending on the achievable scales of the required high magnetic fields. Hopefully, the proposal could provide a platform to detect GWs based on their electromagnetic response in higher frequency bands.

Controllable single-photon routing takes the central roles in optical quantum networks for quantum information processing. Given that most of the schemes previously proposed are specifically designed for the photons with selected frequencies, here we investigate how to implement the routings of single photons with different frequencies. We show that the routing capabilities of the photons with different frequencies are manipulatable by properly designing the configuration of the scatters such as the cavity with embedded atoms and the channel boundaries. This is particularly important to implement the bandwidth routings of photons in future.

The coplanar waveguide (CPW) microwave resonators have been widely applied for solid-state quantum computation and single-photon detection. Based on the physical analysis for the high fidelity readouts of the qubit(s), in this paper we design and then fabricate accordingly the desired aluminum (Al) film quarter-wavelength resonators on sapphire substrates. The ultra-low temperature measurement results show that the linearity of the internal quality factor under the proper driving power is satisfied well for the high fidelity readouts of the qubit(s); and the phase- and amplitude fractional frequency noises are significantly less for avoiding the potential information false alarms of the detected qubit during the readouts. With the demonstrated qubit-resonator experimental parameters, we argue that the designed and fabricated quarter-wavelength CPW resonators, with optimized parameters, can be used to implement the desired weakly perturbing readout measurements of the solid-state qubits on-chip.