Jian-Qi Zhang

Precision measurement of electrical charge with optomechanically induced transparency

We propose a potentially practical scheme to precisely measure the charge number of small charged objects by using optomechanically induced transparency (OMIT) in optomechanical systems. In contrast to conventional measurements based on noise backaction on optomechanical systems, our scheme presents an alternative way to detect the charge number exactly, by monitoring small deformation of the mechanical resonator sensitive to the charge number of nearby charged object. The relationship between the charge number and the OMIT window width is investigated and the feasibility of the scheme is justified by numerical simulation with currently available experimental values.

Tunable double optomechanically induced transparency in an optomechanical system

We study the dynamics of a driven optomechanical cavity coupled to a charged nanomechanical resonator via Coulomb interaction, in which the tunable double optomechanically induced transparency (OMIT) can be observed from the output field at the probe frequency by controlling the strength of the Coulomb interaction. We calculate the splitting of the two transparency windows, which varies near linearly with the Coulomb coupling strength in a robust way against the cavity decay. Our double-OMIT is much different from the previously mentioned double-EIT or double-OMIT, and might be applied to measure the Coulomb coupling strength.

Precision measurement of the environmental temperature by tunable double optomechanically induced transparency with a squeezed field

A tunable double optomechanically induced transparency (OMIT) with a squeezed field is investigated in a system consisting of an optomechanical cavity coupled to a charged nanomechanical resonator via Coulomb interaction. Such a double OMIT can be achieved by adjusting the strength of the Coulomb interaction and can be observed even with a single-photon squeezed field at finite temperature. Since it is robust against cavity decay but very sensitive to some parameters, such as the environmental temperature, the model under consideration can be applied as a quantum thermometer for precision measurement of the environmental temperature within the reach of current techniques.

Tunable multi-channel inverse optomechanically induced transparency and its applications

In contrast to the optomechanically induced transparency (OMIT) defined conventionally, the inverse OMIT behaves as coherent absorption of the input lights in the optomechanical systems. We characterize a feasible inverse OMIT in a multi-channel fashion with a double-sided optomechanical cavity system coupled to a nearby charged nanomechanical resonator via Coulomb interaction, where two counter-propagating probe lights can be absorbed via one of the channels or even via three channels simultaneously with the assistance of a strong pump light. Under realistic conditions, we demonstrate the experimental feasibility of our model by considering two slightly different nanomechanical resonators and the possibility of detecting the energy dissipation of the system. In particular, we find that our model turns to be a unilateral inverse OMIT once the two probe lights are different with a relative phase, and in this case the relative phase can be detected precisely.

Ground state cooling of an optomechanical resonator assisted by a Lambda-type atom

We propose a ground state cooling scheme for an optomechanical resonator based on the system of one Λ-type three-level atom trapped in an optomechanical cavity. This cooling scheme works in a single-photon coupling, and strong atom-cavity coupling regimes. By investigating the cooling dynamics, we find that there is an EIT-like quantum coherent effect in this system which can suppress the undesired transitions for heating. Moreover, our study shows that the final average phonon number of the optomechanical resonator can be smaller than the one based on the sideband cooling. Furthermore, the ground state cooling of the resonator can still be achieved after thermal fluctuations included. In addition, in comparison with previous cooling methods, there are fewer limitations on the decay rates of both the cavity and the atom in this scheme. As a result, this scheme is very suitable to realize the ground cooling of an optomechanical resonator in the experiment.

Fast optical cooling of nanomechanical cantilever with the dynamical Zeeman effect

We propose an efficient optical electromagnetically induced transparency (EIT) cooling scheme for a cantilever with a nitrogen-vacancy center attached in a non-uniform magnetic field using dynamical Zeeman effect. In our scheme, the Zeeman effect combined with the quantum interference effect enhances the desired cooling transition and suppresses the undesired heating transitions. As a result, the cantilever can be cooled down to nearly the vibrational ground state under realistic experimental conditions within a short time. This efficient optical EIT cooling scheme can be reduced to the typical EIT cooling scheme under special conditions.

Cooling a charged mechanical resonator with time-dependent bias gate voltages

We show a purely electronic cooling scheme to cool a charged mechanical resonator (MR) down to nearly the vibrational ground state by elaborately tuning bias gate voltages on the electrodes, which couple the MR by the Coulomb interaction. The key step is the modification of the time-dependent effective eigen-frequency of the MR based on the Lewis-Riesenfeld invariant. With respect to a relevant idea proposed previously (Li et al 2011 Phys. Rev. A 83 043803), our scheme is simpler, more practical and completely within the reach of current technology.

Spatial Landau-Zener-Stuckelberg interference in spinor Bose-Einstein condensates

We investigate the Stuckelberg oscillations of a spin-1 Bose-Einstein condensate subject to a spatially inhomogeneous transverse magnetic field and a periodic longitudinal field. We show that the time-domain Stuckelberg oscillations result in modulations in the density profiles of all spin components due to the spatial inhomogeneity of the transverse field. This phenomenon represents the Landau-Zener-Stuckelberg interference in the space domain. Since the magnetic dipole-dipole interaction between spin-1 atoms induces an inhomogeneous effective magnetic field, interference fringes also appear if a dipolar spinor condensate is driven periodically. We also point out some potential applications of this spatial Landau-Zener-Stukelberg interference.

Generating the Schrödinger cat state in a nanomechanical resonator coupled to a charge qubit

A scheme for generating the Schrodinger cat state based on geometric operations by a nanomechanical resonator coupled to a superconducting charge qubit is proposed. The charge qubit, driven by two strong classical fields, interacts with a high-frequency phonon mode of the nanomechanical resonator. During the operation, the charge qubit undergoes no real transitions, while the phonon mode of the nanomechanical resonator is displaced along different paths in the phase space, dependent on the states of the charge qubit. This generates the entangled cat state between the NAMR and charge qubit, and the NAMR cat state can be achieved after some operations applied on this entangled cat state. The robustness of the scheme is justified by considering noise from environment, and the feasibility of the scheme is discussed.

Efficient cooling of quantized vibrations using a four-level configuration

Cooling vibrational degrees of freedom down to ground states is essential to observation of quantum properties of systems with mechanical vibration. We propose two cooling schemes employing four internal levels of the systems, which achieve the ground-state cooling in an efficient fashion by completely deleting the carrier and first-order blue-sideband transitions. The schemes, based on quantum interference and Stark-shift gates, are robust to fluctuations of laser intensity and frequency. The feasibility of the schemes is justified using current laboratory technology. In practice, our proposal readily applies to a nanodiamond nitrogen-vacancy center levitated in an optical trap or attached to a cantilever.