Single Atoms: Controlling the Quantum World...Single Atoms: Controlling the Quantum World Lecture I:...

Lecture I: Controlling Single Atoms

38th International Nathiagali Summer College on Physics and Contemporary Needs

01. July 2013

D. Meschede, Institut für Angewandte Physik, Universität Bonn

Single Atoms: Controlling the Quantum World


„ ...dass man ebenso wenig

mit einzelnen Atomen

experimentieren kann,

wie wir imstande sind,

Ichtyosaurier in einem Zoo

zu züchten.“

Erwin Schrödinger (1952)


Portrait of a

Single Caesium Atom

A. Alberti, W. Alt, A. Rauschenbeutel, M. Spurny, A. Widera


Why are we interested in controlling neutral atoms?

- Considered 1 of 7 seven potential routes towards

Quantum Information Processing (QIP)

Unique advantages:

* all atoms identical;

* „bottum up“ approach known (this lecture)

* „top down“ approach known (Mott insulators)

Disadvantages:

quantum gates difficult

(= controlled reversible interactions)

Perhaps more importantly:

Illustrating, exploring and controlling the quantum world

Lecture I: Controlling Single Atoms taming?

(c) 2007 ER!K · Personal Entertainment


- Sources of Single Atoms

- Preparing & Moving Atoms

- Single Atom Detection

- Qubits and Adressable Atoms

- Motional Atom Control

- Single Atoms in Ultracold Gases

- Interfering Atom Trajectories










Apparatus for manipulating single neutral atoms

Photon-

Counter

Imaging Optics

MOT-

Laser beams

1 Cs-Atom

1 µm/Pixel


ca. 30 kg copper wire


Real time movies with about 20-50 atoms


Single Atom MOT

0 atoms

1 atoms

2 atoms

3 atoms


500 nm

U0=

1.3 mK z

Wz

Characteristics of the optical dipole potential

MOT

LASER


Laser Sequence

MOT Dipole Trap

N=0

N=2

N=4

N=3

0 10 20 30 40 50

Time [s]

Time (s) 0

1

5

ato

ms

ph

oto

n C

ount

Rate

[ 1

00 k

Hz ]


Moerner, ... Single Ions

Walther, Haroche

1975 1980 1985 1990 1995 2000 2005

Kimble

Ertmer

Meschede

Rempe

Lu

McClelland

Grangier/Browaeys

Chapman

Single Neutral Atoms

Single Molecules

2010

Toschek, .Dehmelt, Blatt, Wineland, ...

Reichel, Kuhr, Saffman, ..


Applications beyond basic quantum physics:

Atom number counting for

ATTA: Atom Trap Trace Analysis (Z. Lu, Argonne; M. Oberthaler, Heidelberg)

Laser-Based Methods for Ultrasensitive Trace-Isotope Analyses (Feature review article)

Z.-T. Lu and K.D.A. Wendt, Review of Scientific Instruments 74, 1169 (2003)










Optical conveyor belt (single atom tweezers)

A O M

A O M

Nd:YAG-Laser

Photon-

Counter

Imaging Optics

MOT-

Laser beams


Frequency

Laser 1

Frequency

Laser 2


"sort" atoms

coupling between

arbitrary pairs of

atoms

Two perpendicular conveyor-belts


initial state:

target state:










Dx Dx


position of

vertical DT

after loading from MOT

after rearranging

six atoms



Light induced chemical reaction

(now called „parity check“)

Could make formation of a single molecule possible …


more controlled motion:

spin dependent transport

P. Jessen , I. Deutsch, PRL 82 (1999), D. Jaksch et al.,ibid.

O. Mandel et al., PRL 91, 010407 (2003); D. Weiss (unpublished)

33



spin dependent transport (Caesium, l = 866 nm)


Position

Tim

e

¼

¼

¼

UEOM

mirror EOM ¸ = 4

experimental

realization

(@ magic wavelength)

inital

final


It works!


2011: transport efficiency in excess of 99%/step!

2009











We need ´perfect` position control: Measuring the house number of the atom

28 29

30 31

32


How to improve the precision for 2 or more neighbouring atoms?

optical instrument

EMCCD

input output

input output


Imaging equation for a sampled light distribution

object

f ( x )

sampling noise

convolution sampling

“inverse” process

deconvolution regularization filtering

blurring

( f ¤ g ) ( x ) ( f ¤ g ) ( x i ) ( f ¤ g ) ( x

i ) + n ( x

i )


44 PRL 102, 053001 (2009)


Distribution of

atoms

Distribution of atom

pairs

45

now called “parity” Used to be “light induced losses”

M. Karski et al., PRL 102, 053001 (2009)










Quantum-Bit (Qubit)

y1

y0

y = ay1 + by0

Classical Bit

1

0

{ 1,0 }

Good atoms have 2 levels only! {↑,↓}


survival probability:

P(F = 3) > 99 %

P(F = 4) < 0.5 % F = 4

F = 3

F´ = 5

"push-out" laser Cs

(1) „Push-out“ technique


Microwave radiation

at 9.2 GHz couples the

up/down quantum states

y1

y0

y = ay1 + by0


Contrast close to 100%, detection efficiency > 90%

Coherence times: Circumstantial! 1 ms < t < 1 s

Rabi oscillations


``HOT´´ atoms COLD atoms

F = 4

F = 3

dCOLD

dHOT

d


t

p/2 p/2

delay

p

p

0 20 40 60 80 100 120 140 160 0

5

10

15

20

25

30

35

40

delay [ms]

po

pu

latio

n in

F=

3 [%

]


0 50 100 150 200 250 300 0

5

10

15

20

25

30

35

40

delay [ms]

p

0 50 100 150 200 250 300 0

5

10

15

20

25

30

35

40

delay [ms]

p

popula

tion in F

=3 [%

]


Controlling neutral atoms:

Tswitch > 16 µs

(mK)


55

0

mF = -4

4

mF = -3

9.2 GHz

F = 4

F = 3 3

Site Selection –

Turn MRI around !

Caesium hyperfine structure

55

Use Microwaves

and B-Field Gradients:


• prepare atoms

• initialize register

• write into register

• read register


The optical lattice spectrum analyzer:

magnetic field gradient maps spectrum into spatial distribution

spin flip spectrum (p-pulse for d=0)



New J. Phys. 12, 065027 (2010).

Beautiful 2D images

by

M. Greiner, Harvard

S. Kuhr/I. Bloch, MPQ

„Quantum gas microscope“ Ref: Physics Today, Oct 2010










… beyond playing marbels with atoms …

Ref: Wikipedia


Displacement

allows microwave

transitions with Dn ≠ 0

High order sidebands! 62

Quantum states

|𝑛, ↑⟩ |𝑛, ↓⟩

Dn = 0 for

identical potentials

carrier transitions only


tunable Franck-Condon/Lamb-Dicke factor!


Microwave Spectroscopy

(associated with dark state cooling, Raman cooling)


Spectral lineshapes are well understood

(transverse motion)


Microwave Cooling



Microwave

Repumping


Cooling removes energy …

… kinetic … … potential …


Coherent Motional Control



70

Coherent excitation for Dn = 1 - 17

70


Motion and Polarization Control



Carrier 1st Blue 2nd Blue

Carrier

1st Blue

2nd Blue

Position on the

Poincaré sphere

defined to

better than 10-3 !


Check for smallest

excitation in sidebands:

This is our sweet

point!

red

blue Even more sensitive

with phases?










• Rb: some 10000 atoms

T ~ 250 nK detection:absorption imaging

• Cs: single atoms

T ~ 30 µK detection: fluorescence



Thermalization of single Cs atoms • Cs cooled to Rb temperature

• Immersion of Cs into Rb gas, strong interaction

• |aRbCs| > 450 Angstrom


3 body collisons limit the

life time of the atoms

N. Spethmann, Thesis (2012)










• Splitting a Single Atom

Position

time

¿

„proto-entanglement“

p/2 pulse

+d shift

+d shift

p pulse

idle

p/2 pulse

+d shift

+d shift

p pulse


single atom interferometer



programming

long

sequences

need coherence!


500:1 !

2011: 10 µm

2012/3: 1 mm ??


Contrast

Phase/2p


86





1-10 atoms for 1 minute

- Optical Conveyor Belts

spin dependent transport, microwave cooling

- Single Atom Adressability

use field gradients/composite pulses

- Single Site Detection

next neighbors resolved!

- Split Atoms with Macroscopic Separations

sensitive single atom interferometer

- Single Impurities for Ultracold Gases

the coldest single atoms?

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