ideas for experimental realization of neutral atom quantum computing
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Ideas for Experimental Realization of Neutral Atom Quantum Computing. 演 講 者:蔡 錦 俊 成功大學物理系 [email protected] http://www.phys.ncku.edu.tw/~cctsai 2002 年 10 月 18 日. Outline. Motivation. Entanglement of two Macroscopic Objects. Trapping and manipulation of Single or Few Atoms. - PowerPoint PPT PresentationTRANSCRIPT
Ideas for Experimental Realization of Neutral Atom Quantum Computing
演 講 者:蔡 錦 俊 成功大學物理系[email protected] http://www.phys.ncku.edu.tw/~cctsai
20022002年年 1010月月 1818日日
OutlineOutline
Motivation
Trapping and manipulation of Single or Few Atoms
Entanglement of two Macroscopic Objects
MotivationMotivationUsing neutral atoms to realize quantum computing
Advantages: Atoms, photons, and fields are involvedWeak interactions with external fieldsMany internal statesLong-lived coherence time
Disadvantages: Exponential decrease of preparing efficiencyNoise and imperfections in setup
Entanglement of two Macroscopic Objects/ Nature 413, 400 (2001), Aarhur, Denmark.
Experimental set-up and the sequence of optical pulses.
Entanglement of two Macroscopic Objects/ Nature 413, 400 (2001), Aarhur, Denmark.
Internal state of neutral Cs atoms and optical pumping
6s 2S1/2
F=4, mF
-4, -3, -2, -1, 0, 1, 2, 3, 4
6p 2P3/2
F=3, mF
-4, -3, -2, -1, 0, 1, 2, 3, 4
+Cs 6s 2S1/2
n=6
l=0
2S+1, S=1/2
J=1/2Nuclear spin, I=7/2F = J+I
Entanglement of two Macroscopic Objects/ Nature 413, 400 (2001), Aarhur, Denmark.
Sample: Two 3x3 cm paraffin coated cells place in a highlyhomogenous B field 0f 0.9 G.Coherence time of spin-state 5~30 msecOptical pumping:Cell1: |F=4, mF=4>; Cell2: |F=4, mF=-4>
Optical pulses: 0.45msec, 0.5 mW at 852 nm with 700 MHz ofblue detuned.
Entangling pulse and verifying pulse are separated by 0.5 msec,no entanglement at 0.8 msec.
Entanglement of two Macroscopic Objects/ Nature 413, 400 (2001), Aarhur, Denmark.
Measurement Cos(t) and Sin(t)
Special variance:
= (Sycos())2 + (Sysin())2
out out
Entanglement of two Macroscopic Objects/ Nature 413, 400 (2001), Aarhur, Denmark.
Normalized special varianceEPR/(Jx) vs. Jx
Below unity level for entangledState of the two atomic samples
Maximum possible entanglement(dotted line)Shot noise of verifying pulse(dashed line)
Degree of entanglement= (35+7)%
Trapping and manipulation of Single or Few AtomsSingle atom trap/ Science 293, 278 (2001), Bonn, Germany
Normal MOT deviceDipole Trap : Nd:YAG laser, =1064nm, counter propagated,Beam waist 0 ~ 30mDipole potential, U(z, t) = U0cos[(t-2z/)] controlled with two acousto-optic modulation (AOM)Detection: position sensitive LIF at Cs F=4 F’=5 and Repumping at F=3F’=4
Advantages for dipole trapping:• Trap all spin states• Very long spin relaxation time ~ 30 sec• High Modulation speed
Trapping and manipulation of Single or Few AtomsSingle atom trap/ Science 293, 278 (2001), Bonn, Germany
Experimental set-up
Trapping and manipulation of Single or Few AtomsSingle atom trap/ Science 293, 278 (2001), Bonn, Germany
Few atoms detection
Good for extracting definite number of neutral atoms from reservoir, Bose-Einstein condensation.
Quantum Tweezer for AtomsDeterministic loading of single atom/PRL 89,70401(2002),Austin,USA
Loading atom from a Condensateand dot potential
The probability of extractinga single atom vs. dot speed. Using1D BEC harmonic trap, N=105 and square dot well.