Research directions

Our research focuses on quantum information and quantum optics based on solid state systems.

Direction one:Quantum computation based on wide bandgap material.

The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid state emitters have emerged as promising candidates with their prospects for on chip integration as quantum nodes and sources of coherent photons for connecting these nodes. In this direction, we are studying the quantum information processing based on wide bandgap material such as silicon vacancy in diamond, GeV in diamond and color center in SiC.

Coherent manipulation of optical transitions in SiV in diamond

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(a) Optical Rabi oscillations using a modulated cw laser and fast detection in the time domain. (b) Rabi frequency is linear with square root of power.(c) The extracted times from the fitting as a function of the excitation laser power. (d) Optical Rabi oscillations for a number of laser detunings. (e) Fourier transform of indicating a Mollow triplet in frequency space.

Production of SiC color center in precise location

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(a) SEM image of aperture arrays with 2-μm cell separation patterned on the surface of the PMMA. (b) SEM image of an approximately 65-nm-diameter aperture patterned on the surface of the PMMA. (c) Confocal image of the sample area with large ionimplantation dose (3000 ions=aperture). (d) Confocal fluorescence image of the sample area with lower ion-implantation dose on the SiC surface. The circled one is the single VSi defect that we study in this paper. The scale bar is 2 μm.

References:

Yu Zhou, Abdullah Rasmita, Ke Li, Qihua Xiong, Igor Aharonovich, Wei-bo Gao Coherent control of a strongly driven silicon vacancy optical transition in diamond Nature Communications 8, 14451

Junfeng Wang, Yu Zhou, Xiaoming Zhang, Fucai Liu, Yan Li, Ke Li, Zheng Liu, Guanzhong Wang, Weibo Gao Efficient Generation of an Array of Single Silicon-Vacancy Defects in Silicon Carbide Phys. Rev. Applied 7, 064021 – Published 16 June 2017

Junfeng Wang, Xiaoming Zhang, Yu Zhou, Ke Li, Ziyu Wang, Phani Peddibhotla, Fucai Liu, Sven Bauerdick, Axel Rudzinski, Zheng Liu, Weibo Gao Scalable fabrication of single silicon vacancy defect arrays in silicon carbide using focused ion beam. ACS Photonics 4.5 (2017) : 1054-1059.

Direction two: Quantum sensing based on SiC color centers.

Quantum sensors with solid state spins have attracted considerable interest due to their advantages in high sensitivity and high spatial resolution. The robustness against environment noise is a critical requirement for solid-state spin sensors. In this direction, we are trying to use spin information in silicon carbide to sense the thermal environment or the magnetic environment.

Self-protected thermometry with infrared photons

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(a) Ramsey fringes at 293.3K. (b) Ramsey oscillation at three different temperature. Fitted f value was given above each curve. (c) Ramsey oscillation frequency as a function of temperature when the microwave frequency ω is fixed. Three points in figure (b) were marked as the same color (blue, pink and black).

References:

Yu Zhou, Junfeng Wang, Xiaoming Zhang, Ke Li, Jianming Cai, Wei-bo Gao Self-protected nanoscale thermometry based on spin defects in silicon carbide Accepted by Phys. Rev. Applied

Direction three: Light-matter interaction based on 2D material.

Compared with monolayer TMD, bilayers have the unique degree of freedom, layers. The additional degree of freedom and spin-valley-layer locking make the system especially interesting for quantum technologies based on spin and pseudospins (Z Gong et al., Nature Communications 4, 2053). The correlation between degrees of freedoms also leads to various exotic physics phenomenon. In monolayer, emission helicity and valley is locked due to spin-orbital coupling and inversion symmetry breaking, which further leads to valley Zeeman splitting. However, in bilayer 2D material, inversion symmetry is recovered, helicity and valley are not locked anymore. It is a natural question to ask whether such valley phenomena still exists in bilayer TMDs. We demonstrate that Zeeman splitting persists regardless of the recovery of inversion symmetry, which comes from spin-valley-layer locking. Zeeman splitting here is present without lifting valley degeneracy, which is in stark contrast to the monolayer case.

Zeeman splitting in bilayer MoTe2

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Zeeman splitting and PL polarization in bilayer MoTe2. a, b Off-resonant polarization-resolved PL spectra taken at −7, 0, and +7 T at 2 K with an excitation energy of 1.560 eV (795 nm) in monolayer MoTe2 (a) for reference and bilayer MoTe2 (b). The excitation is set to σ+ circular polarization. The detection polarization is configured to σ+ (black solid lines) and σ− (red solid lines) circular polarization. The PL intensity of the bilayer is one order of magnitude smaller than that in the monolayer due to higher symmetry of the bilayer. Here the PL spectra is normalized by emission maximum for each particular magnetic field and offset for better visualization. c, d The Zeeman splitting (c) and PL polarization (d) of the neutral exciton (peak A2) in bilayer MoTe2 (red symbols and lines) vs. magnetic field at 2 K. The inset shows the PL polarization at different temperature at +7 T. The black symbols and linesare results of the monolayer (peak A1) for reference. The error bars are calculated from Lorentzian fit of the spectral lines

References:

Chongyun Jiang, Fucai Liu, Jorge Cuadra, Zumeng Huang, Ke Li, Ajit Srivastava, Zheng Liu,and Wei-bo Gao Zeeman splitting via spin-valley-layer coupling in bilayer MoTe2 Nature Communications 8, 802

Near-microsecond valley polarization memory in 2D heterostructures.

Transition metal dichalcogenids (TMDs) have valley degree of freedom and show spin-valley locking, making them promising for valleytronics and platform for quantum computation. For either application, a long valley polarization lifetime is crucial. Previous results show that it is around picosecond in monolayer excitons, nanosecond scale for local exciton and tens of nanosecond for interlayer excitons. Here we show that dark excitons in 2D heterostructures provide a near-microsecond valley polarization memory thanks to the magnetic field induced suppression of valley mixing.

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a, Time-resolved PL with σ+ and σ− output under a pulsed laser excitation with polarization σ+. The left panel shows the decay of the PL emission pumped by σ+ excitation at 0 T while themiddle and the right panel shows the calculated degree of polarization and valley polarization respectively.The degree of polarization disappears quickly and hardly seen after 50 ns and valley polarization has a decaytime of 15 ± 0.3 ns. b, Similar as a, but at a magnetic field of -3 T in the z direction. The PL output difference between the two different polarization can be clearly seen even at 200 ns. Valley polarization has a decay time of 1.745 ± 0.007µs. c, Degree of polarization as a function of Bz with pulsed laser excitation.The intensity is integrated from 21 ns to 7 µs. d, PL polarization as a function of Bz with pulsed laserexcitation. The PL polarization shows linear dependence on magnetic field for small magnetic field beforesaturating at big magnetic field.

References:

Chongyun Jiang, Weigao Xu, Abdullah Rasmita, Zumeng Huang, Ke Li, Qihua Xiong, Wei-bo Gao Microsecond dark-exciton valley polarization memory in 2D heterostructures arXiv: 1703.03133

Direction four: Quantum material investigation.

In this trend, we try to explore exotic quantum materials for the new kind of platforms for quantum information processing. These include the exploration of single photon sources and light matter interaction in perovskite, molecules, and rear earth ions.

Single photon source based on GaN

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a. Schematic illustration of gallium nitride crystal structure and an optical image of the GaN wafer. b, Confocal PL mapping with a single emitter SPE 1 in the centre of the map. c, Photoluminescence spectra of 6 infrared emitters, revealing the PL ranges from 1085 nm to 1340 nm. PL spectra from three emitters are taken at 4 K (upper panel) and 300 K (lower panel), respectively. Note that the emitters at 4K and RT are different. d, Second-order correlation measurement of the emission from SPE 1 under 950 nm cw laser excitation. The blue dots are the raw data without any background correction and the red curve is the fitting to a three level system, yielding g2(0) = 0.05 ± 0.02. e, Second-order correlation measurement of SPE 1 with ~ 1ps laser excitation with 80 MHz repetition rate, yielding g2(0) =0.14 ± 0.01. The g2 measurements were recorded at room temperature.

References:

Yu Zhou, Ziyu Wang, Abdullah Rasmita, Sejeong Kim, Amanuel Berhane, Zoltan Bodrog, Giorgio Adamo, Adam Gali, Igor Aharonovich, Wei-bo Gao Room-temperature solid state quantum emitters in the telecom range arXiv: 1708.04523