Personal Information and education

I was born in 1989, and received a bachelor degree in Electrical Engineering (Xi’an Jiaotong University) in 2012. I chose quantum optics and quantum information as my postgraduate research topic.

In 2012-2017, I studied in the department of Applied Physics as a Ph.D. student. My thesis topic was “Quantum Dynamics in Hybrid Quantum Circuit System With Longitudinal Coupling”. During 2015-2016, I studied in RIKEN, Japan [under the supervision of Prof. Franco Nori)] as an international Ph.D.-joint student. In September 2017, I received my Ph.D. degree.

Research topics

In 2017, I started my lecturer position in the physics department of Xi'an Jiaotong University.

My research now is about quantum control based on hybrid superconducting quantum circuits (SQC) systems. By considering coupling SQC with other artificial quantum plateforms, such as nanomechanical oscillators, surface acoustic waves (SAW) and various types of color-centers, better quantum controls applications could be realized. My present and future reseach topics include:

Mechanical quanta (phonons) can exist in a localized mechanical resonator, phonons SAW cavity or a travelling acoustic wave. Manipulating phonons in quantum level has attracted considerable interest. Possible applications include ultra-sensitive measurements, and testing fundamental quantum mechanics. By coupling these phonon systems with SQC, one can engineer the phonons at quantum level.

In Fig. 1(a), we describe a hybrid quantum system composed of a micrometer-size carbon nanotube (CNT) longitudinally coupling to a flux qubit. Based on this hybrid system, one can generate high-fidelity nonclassical states of motions of a carbon-nanotube via dissipative quantum engineering [__Phys. Rev. B 95, 205415__ (2017)].

In Fig. 1(b), we propose an inverse optomechanical system, in which the frequency of a mechanical mode is effectively modified by a quantized optical field. Compared with a conventional optomechanical system, the role of mechanical and optical modes are exchanged. Based on this hybrid system, one can realize a strong phonon-photon quadratic coupling and demonstrate phonon dynamical Casimir effects.

Fig. 1 (a) By employing the decoherence channel of a flux qubit, one can engineer the motion of a current-carrying carbon nano-tube into macroscopic superposition states. (b) An inverse optomechanical system (IOMS) we proposed. The SAW cavity length is effectively modulated by the microwave field.

**2. Quantum dynamics with longitudinal coupling in SQC**

In recent years, much theoretical and experimental research has been devoted to SQCs based on the so-called longitudinal coupling. Compared with the transverse coupling, the longitudinal coupling describes a completely different quantum mechanism and has its inherent advantages. For example, there is no Purcell decay and residual interactions between a qubit and its resonator.

In Fig. 2(a), we predict that the pure effects of counter-rotating terms in a dipole-dipole-coupling system can be observed, given that the two flux qubits longitudinally couple to a resonator [__Phys. Rev. A 96, 063820__ (2017)].

In Fig. 2(b), we show that the longitudinal freedom of a flux qubit can couple to a bound-tunable measurement resonator. The interaction form is of direct dispersive coupling type. Based on this proposal, one can realize an ideal QND qubit readout without being disturbed by the Purcell effect.

Fig. 2 (a) A proposal to observe pure effects of counter-rotating terms without ultrastrong coupling. (b) A proposal on how to realize an ideal QND readout of a gradiometric flux qubit with a tunable gap. We consider that the qubit couples to a bound-tunable measurement resonator via direct dispersive coulping.

Future projects

1. Quantum transducers between different frequency ranges;

2. Measurement of the virtual excitations in ultra-strong-coupling systems.

Publications

1. X. Wang, A. Miranowicz and F. Nori, Ideal Quantum Nondemolition Readout of a Flux Qubit Without Purcell Limitations, (in preparation).

2. X. Wang, Inverse optomechanical systems, (in preparation).

3. X. Wang, A. Miranowicz, H.-R. Li, Fu-li Li and F. Nori, Two-color electromagnetically induced transparency a mechanical resonator and a qubit, __Phys. Rev. A 98, 023821 (2018)__.

4. W.-X Liu, X. Wang, M.-M. Luo, X.-J. Sun, S.-Y. Gao and F.-L. Li, Dipole induced transparency and Aulter–Townes splitting via a dipole emitter coupled to a hybrid photonic-plasmonic resonator, __J. Opt. 20, 105401 (2018)__

5. X. Wang, A. Miranowicz, H.-R. Li, and F. Nori, Observing pure effects of counter-rotating terms without ultrastrong coupling: A single photon can simultaneously excite two qubits, __Phys. Rev. A 96, 063820__ (2017).

6. W. Qin, X. Wang, A. Miranowicz, Z.-R. Zhong, and F. Nori, Heralded quantum controlled phase gates with dissipative dynamics in macroscopically-distant resonators,__ Phys. Rev. A, 96, 012315__ (2017)

7. W.-X. Liu, X. Wang, Y.-Q. Chai, S.-Y. Gao, and F.-L. Li, Multiple plasmon resonance in a concentric silver-atomic medium nanoshell, __J Appl. Phys. 121, 123102__ (2017)

8. X. Wang, A. Miranowicz, H.-R. Li, and F. Nori, Hybrid quantum device with a carbon nanotube and a flux qubit for dissipative quantum engineering, __Phys. Rev. B 95, 205415__ (2017).

9. X. Wang, H. Chen, C.-Y Li, and H.-R. Li, Vibration-assisted coherent excitation energy transfer in a detuned dimmer, __Chin. Phys. B 26 (3), 037105__ (2017).

10. X. Wang, A. Miranowicz, H.-R. Li, and F. Nori, Multi-output microwave single-photon source using superconducting circuits with longitudinal and transverse couplings, __Phys. Rev. A 94, 053858__ (2016).

11. H. Chen, X. Wang, A. P. Fang and H. R. Li, Phonon-assisted excitation energy transfer in photosynthetic systems, __Chin. Phys. B, 25 098201 (2016)__

12. X. Wang, A. Miranowicz, H.-R. Li, and F. Nori, Method for observing robust and tunable phonon blockade in a nanomechanical resonator coupled to a charge qubit, __Phys. Rev. A 93, 063861__ (2016).

13. X. Wang, H. R. Li, D. X. Chen, W. X. Liu, and F. L. Li, Tunable electromagnetically induced transparency in a composite superconducting system, __Opt. Commun. 366, 321__ (2016).

14. X. Wang, H.-R. Li, P.-B Li, C.-W. Jiang, H. Gao, and F.-L. Li, Preparing ground states and squeezed states of nanomechanical cantilevers by fast dissipation, __Phys. Rev. A 90, 013838__ (2014).

Funding and support

2015-2016 The National Scholarship for Ph.D. joint student; China Scholarship Council (CSC);

2017-2020 “Detecting the ground-state photons in ultra-strong coupling SQC via parametrical tunable coupling”, China Postdoctoral Science Foundation, Grant No. 2018M631136;

2018-2021 “Quantum Nondemolition measurement of virtual excitations in ultrastrong coupling systems”, National Natural Science Foundation of China (NSFC), Grant No. 11804270.