Welcome to Microcavity Group

Microcavities
 

microcavities_a_gmail.com
 

 

1 Photon Source

1.1 Single photons from single quantum dot or NV center in diamond with the interaction with micro-cavity, nano-wire or metal surface Plasmon

1.2 Two photons from micro-cavity parametric down conversion

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Figure 1:
Schematic illustration of setup to generate an on-chip polarization entangled photon source. The micro-disk with integrated pump laser is used to prepare two-photon states, which can be transformed to polarization entangled photon states by the coupling waveguide and the on-chip polarization beam splitter.

2 Transmission and linear optical operation

2.1 On-chip interferometer with optical waveguides and nano-wires

2.2 Surface Plasmon assisted polarization operations

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Figure 2:
Schematic illustration of the integrated surface plasmon based polarization beam splitter. Field distribution of (a) the PBS and (b) the 1=3 PBS with TE or TM polarization input at Port 1.

2.3 Optical filters with micro-cavity

3 Photon-photon interaction with micro-cavity QED

3.1 Fabrication of micro-cavity with diamond, silica and other materials:

WGMs micro-cavities made by silica materials can reach ultrahigh Q through thermal reflow process. In sphere and toroid micro-cavity, the Q factor can reach 1 0 7 ~ 1 0 8 , because thermal processing makes ultra-smooth cavity boundary and decreasing the scatting loss of cavity. Benefiting from the ultrahigh Q, there's lots of applications, for example ultra-low threshold lasing, nonlinear experiments, sensing. The high quality factor property also imply a low dissipation which supports a way to strong coupling in QED experiments combing with narrow spectrum emitter (such as cold atom).
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Figure 3:
Microsphere fabrication setup (A) and process (B)
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Figure 4:
XeF2 etch setup for silica microdisk and microtoroid on silicon chip
Excepting for silica based micro-cavities, other materials are also tried to fit for QED experiment, such as PMMA poly spheres, hybrid spheres with coating material and other hybrid structures. Embedding quantum emitter (such as quantum dot, atom, color center) in these kind of cavities is achievable, it not only makes a stable solid-state system, but also can position emitter in mode maximum field in cavity, which will increase g factor between emitter and field. Furthermore for NV centers, the ones in single diamond crystal have better quantum properties, at this motivation, we also directly make cavities on diamond for QED research basing diamond.
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Figure 5:
Diamond disk fabrication. (a) fabrication process and (b) SEM image of a polycrystal diamond disk

3.2 Fabrication of NV centers in diamond:

Fabrication color centers in nano-photonic structures in demand position is important. In order to get strong coupling with optical field, it's better to control NV centers position overlap with maximum electromagnetic field in cavity mode. Embedding color centers in diamond with structure also can obtain a stable solid state system in application, makes building complex system possible. For quantum technologies, the single NV center in position and long spin coherent time are urgent needed for artificial NV centers. Implanting nitrogen ion to diamond can create NV centers, combining with nano-fabrication technology, we try to archive the demand properties.
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Figure 6:
Fabrication and measurement of NV centers lattice. (a) Illustration of nitrogen-ion implantation with PMMA coating. (b) ODMR spectrum of NV centers in the lattice. (c) and (d) Fluorescent emission from confocal scanning with the diameters of the holes in PMMA coating of 100nm and 50 nm, respectively. In (d), the point in the circle was used in the measurement of ODMR and Rabi oscillation.

3.3 Detection

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Figure 7:
Fiber taper coupling scheme. (A) is the schematic and (B) is the corresponding setup.
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Figure 8:
Free space coupling scheme. (a) is the schematic, inset illustrates the CCW and CW modes coupling, (b) bright spot A from CCW mode can be detected when tunable laser is on microcavity resonance.

4 Quantum Controll of Nitrogen-Vacancy Center in Diamond

The negatively charged nitrogen-vacancy (NV) center in diamond is one of the most suggested systems for quantum computers. The center forms a triplet spin state, the spin-selective relaxation and fluorescence make it possible to optical polarization and detection, further more the electron spin state can be coherently manipulated with resonance microwave pulse sequences. If we use the electron spin state as qubit, then we can achieve the single qubit gates with a single NV center.
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Figure 9:
 
 
 

Copyright 2009 All Rights Reserved microcavities_a_gmail. com Last Modified 22/08/2012 by Jinming Cui

University of Science & Technology of China, Key Lab of Quantum Information, CAS