Single atoms in rotating ring optical lattices
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KITPC: Condensed Matter Physics of Cold Atoms ---- Optical Lattices II. Single Atoms in Rotating Ring Optical Lattices. Mingsheng ZHAN ( 詹明生 ) State Key Lab of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, CAS

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Single Atoms in Rotating Ring Optical Lattices

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KITPC: Condensed Matter Physics of Cold Atoms ---- Optical Lattices II

Single Atoms in Rotating Ring Optical Lattices

Mingsheng ZHAN (詹明生)

State Key Labof Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, CAS

Center for Cold Atom Physics, CAS

Oct 15, 2009 Beijing


Motivation

  • quantum simulation

  • quantum computing

  • single photon source

  • single atom physics


quantum simulation mimic an unknown system using a controllable system


Hubbard model

Approximate model that describes electrons in solids

Hamiltonian describes fermions /bosons in a periodic potential

Simple, yet hard to solve analytically, numerically or empirically

X

J

U

i=1

i=2

i=3

i=4

i=5

John C. Hubbard

at 1963

J tunneling U in site interactionexternal potential


Quantum logic gates

  • Need of experimental aspects:

  • single atoms

  • cooled to ground state

  • double-well

  • readout

U.Dorner, T.Calarco, P.Zoller, A. Browaeys and P. Grangier,

J. Opt. B: Quantum Semiclass. Opt. 7 (2005) S341–S346


Atom array by dipole trap

(bottom-up)

Ultracold atoms in lattices

(top-down)

single atom

dipole trap

array

cooling the array

ultracold gas

optical lattices

addressing individual atoms

The same goal by different routes (殊途同归)

(for quantum simulation)


Optical Dipole Trap for Atoms

Atom

Laser

Cylindrically

symmetric

harmonic

oscillator


Superfluidity limit

+

+

+

+

Good phasei,

but Poissonic number


Mott Insulator State

Fockstate

+

+

+

+

good number,

But no phase

M. Greiner, O. Mandel, T. Esslinger, T. Hansch, I. Bloch,

Nature 415 (2002) 39.


P.Grangier’s group[IO/CNRS]


"Collision blockade”

RE: Radiative Escape process

FCC: Fine-structure Changing Collision

Phys. Rev. Lett. 89, 023005 (2002)

Nature 411, 1024 (2001).


D.Meschede’s group[Bonn Univ.]


The single atom trap @ WIPM


Vacuum

system

dichromatic

mirror

830/852nm

Filter

780nmfluor.

MOT laser

Single Atom Trap @ WIPM

experimental setup

87Rb

MOT 780nm

dipole trapping 830/852nm


Fluorescence of a single Rb atom (2009/02/13)

1 atom

0 atom

10s

2 atom

1 atom

0 atom


Hanbury Brown and Twiss (HB-T) effect

classical field

non-classical

thermal

coherent

single photon

Fluorescence of single atom, antibunching:

http://en.wikipedia.org/wiki/Hanbury-Brown_and_Twiss_effect

M.O.Scully and M.S.Zubairy, Quantum Optics, CUP 1997, P.307


TTL

BS

Fiber

SPCM

Discriminator

NIM

SPCM

Trigger

Δt

Discriminator

TTL

NIM

Single Atom HBT Experiment

Coincidence

SPCM: EG&G SPCM-AQRH-14-FC

Discriminator:ORTEC 935(Quad 200-MHz Constant-Fraction Discriminator)

Coincidence: RoentDek TDC8HP


HBT measurement of single atom

in dipole trap

[email protected]

[email protected]

[email protected]

AC shift 39MHz

U01.9mK

Rabi Freq 0

26.6MHz(RL)

33.7MHz(CL22)

79 MHz(CL23)

107 total events

103 coincidence

Photon antibunching

(single atom)


lifetime of the single atom trap

Time sequence

threshold

Counting

1) once counting > threshold,

freezing the trap;

2) waiting a time Δt, then

check; repeat 100 times;

3) new Δt, then repeat.

Δt

ON

OFF

Cooling and

repump laser

50ms

ON

OFF

MOTmagnetic field

ON

OFF

Counting clock

ON

OFF

Dipole trap laser


Lifetime 468ms

with MOT on

Lifetime 11s

with MOT off


Ring Optical Latticesby SLM


Laguerre-Gaussian Mode


Ring Optical Lattice (ROL)

Superposition of the mode


Realizing ROLwith a spatial light modulator (SLM)

SLM


0th order

1th order

modulated


Trapping atom array with ROL

Single trap

Double

trap

Spatial filter


Rotating the ROL


Rotating ROL

Scheme 1: max 60Hz

Continuous phase pattern animation on the SLM, max refresh rate 60Hz


Scheme 2: up to MHz (EOM driven phase change)

2Hz rotation is shown here


single atoms in rotating ROL

Rotating ROL @12Hz

with 1 atom

Rotating ROL @6Hz

with 2 atoms

Xiaodong He, Peng Xu, Jin Wang and Mingsheng Zhan, Opt.Express (accpted, 2009)


Dynamics of single atoms in the traps


Loading two atoms to a trap

Ring trap

Gaussian trap


Light assisted nonelastic collisions of two atoms in a trap

In a Ring trap

Collisions rare

Difficult to meet

2 atoms remain

In a Gaussian trap

0 atom

Collisions rich

Easier to meet

1 atom

MOT light on


Splitting a trap (with an atom) to two traps

or

Potential or force? (single vs multi: collision)

Particle or wave packet? (single atom interferometer)


Figure 12. Axial insertion. An atom trapped in one of the potential wells of the standing wave of theVDT is inserted into the Gaussian potential well of the HDT by axially moving the VDT along the z-direction.

Figure 13. Radial insertion of an atom. (a) An atom in the VDT after the extraction. The traps are separated by displacing the HDT along the x-direction. (b) The atom in the VDT is transported to the z-position of the HDT. (c) The

traps are merged by moving the HDT along the x-direction towards the VDT. d) Evolution of the radial potentials of the traps along the x-axis for steps (b) and (c).

Y Miroshnychenko et al.,

NewJ.Phys.8(2006)191


Moving trap

Static trap

?

dichroic mirror

Static trap

fluorescence

Moving trap

To SPCM

PZT

PZT scan speed: 10um/40ms

160ms

Cooling&Repump

80ms

5V

PZT

-2V

The depth of the moving well affects the rate carrying the atom


Time evolution of the trap intensity profile

Initial

?

The final position of the atom is determined by force

not the depth of potential.

exposure time 1ms readout time 2.5ms


Atom transfer between traps

Gaussian trap

Merging

Splitting

ring trap


Time sequence:

double  Gaussian  double

On

Interaction time: N*1/60 s

N =1,2,3 …variable

Cooling light

repumping light

MOT coil

Off


Time sequence:

double  ring  double

On

Interaction time:N*1/60 s

N =1,2,3 …variable

Cooling light

repumping light

MOT coil

+ L (or – L) SLM light

Off


2

1

Single atom transport(via a Gaussian trap)

1/60 s

3/60 s


Single atom transport(via a ring trap)

2

1

1/60 s

3/60 s


Next …

  • cooling atom to ground state + internal state control

  • making interaction of atoms in/between sites

  • entanglement, quantum simulation / computing ……

  • single atom AI, HBT…


a way to bring the atoms closer—— optical vector beam (OVB)


Optical vector beam(OVB)

  • The focused pattern can be much smaller than the diffraction limit

Tailoring of arbitrary optical vector beams

New Journal of Physics 9 (2007) 78

Phys. Rev. Lett. 91, 233901 (2003)

Phys. Rev. Lett. 100, 123904 (2008)


Experimental Arrangement

HW

PW

to trap

PBS

SLM

HW

HW

Dipole trap laser


Primary results with OVB

OVB trap

Lifetime longer

Tighter potential

Normal ring trap

Lifetime shorter


Acknowledgments

许鹏 何晓东

王谨 刘敏

Ministry of Sci & Tech of China (MOST)

Chinese Academy of Sciences (CAS)

Natural Science Foundation of China (NSFC)

All of you, for your attention!


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