2017 Fiscal Year Annual Research Report
Developing a fiber optical quantum interface using trapped atoms and nanofiber based photonic crystal cavity
| Project/Area Number |
15H05462
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| Research Institution | The University of Electro-Communications |
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Principal Investigator |
Nayak K.Prasanna 電気通信大学, フォトニックイノベーション研究センター, 特任准教授 (70551042)
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| Project Period (FY) |
2015-04-01 – 2019-03-31
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| Keywords | Quantum Optics / Nanophotonics / Optical Nanofiber / Cavity QED / Quantum Information |
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| Outline of Annual Research Achievements |
The purpose of the research is to develop a fiber optical quantum interface using nanofiber based photonic crystal cavity. In this project we will develop an optical tweezer based single-atom trap near the nanofiber cavity so that deterministic quantum state-transfer between single atom and photons can be realized.
In FY2015 and FY2016, we have succeeded in trapping single atoms in optical tweezer. However, loading the trapped single atoms to the nanofiber trap was not achieved. We attribute this issue to the interaction of trapped atoms with the nanofiber surface. In FY2016, we have successfully fabricated a centimeter-long cavity on the nanofiber which can operate in both Purcell and strong-coupling regimes of cavity QED with high transmission. In FY2017, we have succeeded in trapping and probing atoms in a two-color guided mode trap around the nanofiber. This inherently mitigates the issues related to atoms sticking to the nanofiber surface. Moreover, we have succeeded in installing high quality nanofiber cavity into the vacuum chamber and stabilizing the cavity mode to the atomic line under ultra-high vacuum conditions.
The objective for FY2018, is to investigate cavity QED experiments with single atoms trapped in a two-color guided mode trap around the nanofiber segment of a centimeter-long nanofiber cavity.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In FY2017, we have first targeted the issue of atom-surface interaction. We have found that, in order to keep the atoms away from the nanofiber surface, it is essential to send few mW of blue-detuned light (at a wavelength of 830 nm) through the nanofiber. Therefore, we have adopted a two-color guided mode trap for trapping atoms around the nanofiber. We have also developed a technique to filter the background fluorescence from the fiber material induced by the trapping light, by using volume Bragg gratings and solid etalons. This has enabled the measurement of absorption of a weak guided probe field by a few atoms trapped around the nanofiber.
We have succeeded in the installation of high quality centimeter-long photonic crystal (PhC) nanofiber cavity into the vacuum chamber. We have established a technique to send few mW of trapping light through the PhC nanofiber cavity under ultra-high vacuum (UHV) conditions, without seriously damaging the PhC structure.
Stabilizing the cavity mode of a centimeter-long nanofiber cavity to the atomic line, under UHV conditions, is technically challenging due to the thermal drift of the PhC cavity induced by the locking light itself and vibration of the nanofiber. We have successfully developed a technique to stabilize the cavity using a dual-mode locking scheme.
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| Strategy for Future Research Activity |
In FY2018, we will investigate cavity QED experiments with single atoms trapped in a two-color guided mode trap. For this experiments, we will be using a centimeter-long nanofiber cavity which can operate in both Purcell and strong-coupling regimes of cavity QED with high transmission. The following experiments will be performed.
a) Spectroscopy of the atom-cavity system. The transmission and reflection spectra of the atom-cavity system will be measured using a weak probe laser through the guided mode. The modification of the spectra based on the atom-cavity coupling strength will be investigated for cavity modes operating in different regimes of cavity QED.
b) Pi-phase flip of the reflected light. The phase of the reflected light will be measured using an interferometer scheme in the reflection port. This will reveal the Pi-phase flip of the reflected photon in the presence of a single atom resonantly coupled to the nanofiber cavity.
c) Channeling efficiency into the nanofiber guided modes. The fluorescence photons from the trapped atom coupled to the nanofiber cavity will be measured for different cavity modes. The dependence of the photon count rates on the cavity linewidths will reveal the enhancement of the channeling efficiency into the nanofiber guided modes.
d) Modification of the decay rate of the atom in the nanofiber cavity. The temporal dynamics of the fluorescence photons coupled to the nanofiber cavity will be measured for different cavity modes. This will further clarify the atom-cavity coupling strength and hence the cooperativity.
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