Quantum entanglement between two antiferromagnets in the microcavities

Mangons are newly developed as the qubits for quantum storage and information process. Here in this work, we focus on a hybrid quantum system containing two antiferromagnets, and the entanglement between magnons in the antiferromagnets could be generated through the strong coupling mediated by the same microwave mode. Moreover, we numerically simulated the process with the feasible parameters. And the influence of the system parameters, such as the magnon-photon coupling rate, the detuning, the bias magnetic field and the dissipation on the entanglement are discussed. By adjusting some of the experimental parameters, we show that two antiferromagnets can produce a large entanglement, which is a result that has not been found in other quantum systems before. Our findings may provide a potential platform for the completion of related quantum tasks in the future.

Large cooperativity in strongly coupled chip-scale photonic-atomic integrated system

The miniaturization of atomic quantum systems and their integration into silicon microchips paves the way for a wide variety of applications in quantum computing, metrology and magnetometry. A particular interest is found in the integration of quantum entities into the micro and nanoscale photonic resonators to implement chip scale cavity quantum electrodynamics. Here we demonstrate the interaction of a chip scale micro disc resonator with thermal rubidium atoms via the evanescent field of the mode. We observe high Rabi splitting of 4 GHz in the transmission spectrum of the coupled photonic-atomic system due to collective enhancement of the coupling rate by the ensemble of hot atoms and present a theoretical model to support the measured results. This result corresponds to atom-photon cooperativity of ~ 1. Such cooperativity is the onset for quantum interference, needed for high-end chip scale quantum technologies, such as such as quantum manipulation, quantum information storage and processing, and few photon switching.

Design and analysis of a low crosstalk error nested structure two-dimensional micro-displacement stage

In order to solve the low coupling displacement and high crosstalk error of multi-dimensional micro-displacement stage, a two-dimensional micro-displacement stage based on flexure hinges and piezoelectric ceramics is designed and analyzed. The whole stage adopts a nested parallel structure. The design parameters of flexure hinges are calculated using Pseudo-rigid body model. Those parameters are confirmed by a simulation before manufacturing the stage. A double frequency laser interferometer is used for measuring the displacement and crosstalk error of the stage when it’s driven. The experimental results show that the maximum crosstalk error of the two-dimensional displacement platform within full travel is 0.98%, the displacement coupling rate approaches 91.4%, and the remaining trajectory deviation caused by hysteresis asymmetry can be reduced to 0.79%.

Large flux-mediated coupling in hybrid electromechanical system with a transmon qubit

Control over the quantum states of a massive oscillator is important for several technological applications and to test the fundamental limits of quantum mechanics. Addition of an internal degree of freedom to the oscillator could be a valuable resource for such control. Recently, hybrid electromechanical systems using superconducting qubits, based on electric-charge mediated coupling, have been quite successful. Here, we show a hybrid device, consisting of a superconducting transmon qubit and a mechanical resonator coupled using the magnetic-flux. The coupling stems from the quantum-interference of the superconducting phase across the tunnel junctions. We demonstrate a vacuum electromechanical coupling rate up to 4 kHz by making the transmon qubit resonant with the readout cavity. Consequently, thermal-motion of the mechanical resonator is detected by driving the hybridized-mode with mean-occupancy well below one photon. By tuning qubit away from the cavity, electromechanical coupling can be enhanced to 40 kHz. In this limit, a small coherent drive on the mechanical resonator results in the splitting of qubit spectrum, and we observe interference signature arising from the Landau-Zener-Stückelberg effect. With improvements in qubit coherence, this system offers a platform to realize rich interactions and could potentially provide full control over the quantum motional states.

Inelastic Processes in Copper-Hydrogen Collisions Including Fine Structure Effects

Inelastic processes in low-energy Cu + H and Cu+ + H− collisions, such as mutual neutralization, ion-pair formation, excitation, and de-excitation, 306 partial processes in total, are investigated taking fine structure effects into account. We use the asymptotic approach to model the adiabatic potentials and adapt a recently proposed method to include the copper fine structure. The nuclear dynamics is performed by making use of the multichannel analytical approach and the Landau-Zener model. The rate coefficients are calculated for the temperature range 1′000 − 10′000 K. The largest rate coefficient is obtained for the mutual neutralization process Cu+ + H− → Cu(3d105s 2S1/2) + H with a value of 3.81 × 10−8 cm3/s at a temperature of 6′000 K. The next lower rate coefficients with values below 10−8 cm3/s correspond to the partial processes of mutual neutralization ${\rm Cu}^{+} + {\rm H}^- \rightarrow {\rm Cu}(3d^{10}5p~^2P^{\circ }_{3/2, 1/2}) + {\rm H}$, Cu+ + H− → Cu(3d104d 2D3/2, 5/2) + H, and the de-excitation process ${\rm Cu}(3d^{10}4p~^2P^{\circ }_{1/2}) + {\rm H} \rightarrow {\rm Cu}(3d^{9}4s^2~^2D^{\circ }_{3/2, 5/2}) + {\rm H}$. It is shown that the practice to redistribute LS-coupling rate coefficients among fine structure sublevels can give rates which deviate significantly from those calculated in the JJ-coupling scheme, that is, with account for the fine structure effects.

Sideband-resolved resonator electromechanics based on a nonlinear Josephson inductance probed on the single-photon level

Light-matter interaction in optomechanical systems is the foundation for ultra-sensitive detection schemes as well as the generation of phononic and photonic quantum states. Electromechanical systems realize this optomechanical interaction in the microwave regime. In this context, capacitive coupling arrangements demonstrated interaction rates of up to 280 Hz. Complementary, early proposals and experiments suggest that inductive coupling schemes are tunable and have the potential to reach the single-photon strong-coupling regime. Here, we follow the latter approach by integrating a partly suspended superconducting quantum interference device (SQUID) into a microwave resonator. The mechanical displacement translates into a time varying flux in the SQUID loop, thereby providing an inductive electromechanical coupling. We demonstrate a sideband-resolved electromechanical system with a tunable vacuum coupling rate of up to 1.62 kHz, realizing sub-aN Hz−1/2 force sensitivities. The presented inductive coupling scheme shows the high potential of SQUID-based electromechanics for targeting the full wealth of the intrinsically nonlinear optomechanics Hamiltonian.

Large Flux-Mediated Coupling in Hybrid Electromechanical System With A Transmon Qubit

Control over the quantum states of a massive oscillator is important for several technological applications and to test the fundamental limits of quantum mechanics. Addition of an internal degree of freedom to the oscillator could be a valuable resource for such control. Recently, hybrid electromechanical systems using superconducting qubits, based on electric-charge mediated coupling, have been quite successful. Here, we realize a hybrid device, consisting of a superconducting transmon qubit and a mechanical resonator coupled using the magnetic-flux. The coupling stems from the quantum-interference of the superconducting phase across the tunnel junctions. We demonstrate a vacuum electromechanical coupling rate up to 4 kHz by making the transmon qubit resonant with the readout cavity. Consequently, thermal-motion of the mechanical resonator is detected by driving the hybridized-mode with mean-occupancy well below one photon. By tuning qubit away from the cavity, electromechanical coupling can be enhanced to 40 kHz. In this limit, a small coherent drive on the mechanical resonator results in the splitting of qubit spectrum, and we observe interference signature arising from the Landau–Zener–Stückelberg effect. With improvements in qubit coherence, this system offers a novel platform to realize rich interactions and could potentially provide full control over the quantum motional states.