2015 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 |
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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 |
We have constructed the new vacuum system for laser cooling which incorporates an aspheric lens for the optical tweezer. The aspheric lens tightly focuses the trapping laser (wavelength: 938 nm) down to 1.5 um beam waist and it also collects the fluorescence of the trapped single atom (wavelength: 852 nm). The tweezer is scanned using two galvo mirrors. We have developed the experiment control system using FPGA based counters. Now the experiments can be triggered by the single atom fluorescence signal. This opens various possibility to manipulate the trapped single atom. Using such a setup we have succeeded in trapping single Cs-atoms in a magic wavelength optical tweezer of 1 mK trap depth. The measured trap lifetime is around 2.4 s. Using polarization gradient cooling, we have realized effective temperature of single atom in the trap down to 20 uK. We have also succeeded in transporting the trapped single atoms over 50 um within few millisecond time scale.
We have also installed photonic crystal nanofiber cavity into the vacuum system. The nanofiber holding structure is equipped with Attocube system to stretch the nanofiber cavity. By stretching the nanofiber cavity we have realized coarse tuning of the cavity mode over 10 nm and the fine tuning range is 180 GHz. In this way we have tuned the cavity mode to the Cs-atom transition at 852 nm.
Using the above mentioned single atom transport technique we have attempted to load the trapped atom to the nanofiber trap. However, we have not succeeded in loading the trapped atom to the nanotrap near the nanofiber surface.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
We have succeeded in trapping and manipulating single atoms in optical tweezer. However, we have not succeeded in loading the trapped single atoms to the nanotrap near the nanofiber surface. The following are the possible reasons for it.
One of the technical difficulty that we realized is the vibration of the nanofiber inside the vacuum chamber. We have measured the auto-correlation of the tweezer light scattered into nanofiber guided mode. From this we have estimated the vibration amplitude of 600 nm and vibration frequency of 570 Hz. Although the vibration frequency is smaller than trap frequencies of 7 kHz (axial) and 53 kHz (radial). However, the vibration amplitude is significant compared to the tweezer beam waist of 1.5 um which may account for loss of atom during the loading process.
Also we have investigated the loading procedure using FDTD simulations. When the tweezer beam is scanned on to the nanofiber the free-space trapping potential modifies to standing wave like nanotrap due to reflection from the nanofiber. If this transition occurs gradually then the atoms can be adiabatically loaded to the nanofiber trap. From the simulations we have realized that by using thinner nanofiber (around 300 nm in diameter) the atoms can be adiabatically loaded to the nanofiber trap. For the present fiber diameter of 500 nm, this loading process shows some discontinuity which might be a reason for the escape of atoms during the loading process.
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| Strategy for Future Research Activity |
The research plan for FY2016 are the followings. 1) Trapping single atoms near the nanofiber cavity. For successful loading to nanofiber trap, we will develop the fabrication of thinner nanofiber (around 300 nm diameter) with high transmission. Moreover, we will modify the nanofiber holding structure to overcome the vibration issue.
2) Cavity QED experiments with trapped single atom near nanofiber cavity. After succeeding in trapping single atoms near the nanofiber cavity, we will demonstrate single-atom based cavity-QED experiments. The coupling strength (cooperativity) between single-atom and cavity will be quantified by measuring the excited state lifetime of the trapped atom.
3) Atom-Photon quantum gate. We are aiming at a cooperativity of 10-20. In this regime a single resonant atom can block the cavity transmission and the photons are mostly reflected without entering the cavity. Moreover, the reflected photon will have a Pi-phase difference compared to the case when there is no atom. Based on this concept, we will demonstrate a quantum phase gate.
For this experiment the atomic (qubit) state preparation is crucial. We will be using microwave based optical pumping scheme for the qubit state preparation.
4) Preparation for homodyne detection. We will postpone the plan for optical cat-state generation and QND measurements to FY2017. However, we will develop the homodyne detection setup which will be the main requirement for those experiments.
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Research Products
(6 results)
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[Presentation] Poster Presentation: Atom Entanglement in Nanophotonic Cavity QED2015
Author(s)
P. Samutpraphoot, T. Peyronel, C. Senko, M. Endres, A. Keesling, J. Thompson, T. Tiecke, K. P. Nayak, V. Vuletic, M. Lukin
Organizer
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics (DAMOP 2015)
Place of Presentation
Ohio, USA
Year and Date
2015-06-08 – 2015-06-12
Int'l Joint Research
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