quantum memory with 3-level atoms - ifraf · arc centre of excellence for quantum atom optics the...

ARC Centre of Excellence for Quantum Atom OpticsThe Australian National University

Canberra, Australia

Quantum memorywith 3-level atoms

G. Hétet, M Hosseini, B. M. Sparkes, J. J. Longdell, M. J. Sellars, M. T. L Hsu, P. K Lam and B. C Buchler

SCTPO IQ U A MUTN

A UN

Research School of Physical SciencesThe Australian National University

Canberra, Australia

Les Houches 2009

Quantum Memory

Suppose you have a quantum state of light......

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Quantum Memory

Squeezed state

Schrödinger cat state


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Quantum Memory

Squeezed state



You can only store it in a memory that does not measure the state.

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Uses:Quantum cryptographyQuantum computing

Quantum Memory

Squeezed state



You can only store it in a memory that does not measure the state.

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Quantum Memory Overview

• Electromagnetically induced transparency (EIT)

• Delay of squeezed light & entanglement with EIT

• Photon echos and Gradient Echo Memory

MahdiHosseini

BenSparkes

GabrielHétet

Ping KoyLam

JevonLongdell(Otago)

MattSellars(SSS Group, ANU)

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ˆ E (z,t)

EIT in a 3-level atom

• The field Ωc is used to control the transmission of E. *

•There is no noise added to E by EIT provided population shuffling is negligible**.

**Hetet et al. Phys. Rev. A 77 012323 (2008)* Ex : Harris , Phys. Rev. Lett. 64 1107 (1990)

!1.0 !0.5 0.0 0.5 1.0!1.0

!0.5

0.0

0.5

1.0

!1.0 !0.5 0.0 0.5 1.00.0

0.5

1.0

1.5

2.0 Amplitude

Phase

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ˆ E (z,t)

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Ω c ( t )

EIT in a 3-level atom

• The field Ωc is used to control the transmission of E. *

•There is no noise added to E by EIT provided population shuffling is negligible**.

**Hetet et al. Phys. Rev. A 77 012323 (2008)* Ex : Harris , Phys. Rev. Lett. 64 1107 (1990)

!1.0 !0.5 0.0 0.5 1.0!1.0

!0.5

0.0

0.5

1.0

!1.0 !0.5 0.0 0.5 1.00.0

0.5

1.0

1.5

2.0 Amplitude

Phase

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∂∂t− vg (t)

∂∂z

ψ(z,t) = 0

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ψ = a(t)Ε + b(t)α

The EIT normal mode

• The normal mode (polariton) is a mixture of atomic polarisation and optical field.

• It’s evolution can be manipulated via the control beam.

Fleischhauer and Lukin, PRL 84 5094

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Squeezed state delay in EIT.

Hetet et al. Opt Express 16 pp. 7369 (2008)

Squeezed source at 795nm and EIT in warm 87Rb vapour. See also:Appel et al. PRL 100, 093602 (2008)Honda et al., PRL 100, 093601 (2008),

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X̂+

X̂!

!X̂+

!X̂!

Amplitude quadrature uncertainty

Phase quadrature uncertainty

The ball represents the noise over some frequency band. The stick represents the coherent amplitude at

the carrier frequency.

Squeezed states

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Bright minimum uncertainty state

X̂+

X̂!

Squeezed states

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X̂+

X̂!

Bright phase squeezed state

Squeezed states

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X̂+

X̂!

Bright amplitude squeezed state

Squeezed states

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X̂+

X̂!

Bright amplitude squeezed state

Squeezed states

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X̂+

X̂!

Vacuum squeezed state

Squeezed states

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X̂+

X̂!

Vacuum squeezed state

Vacuum state

Squeezed states

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Squeezing transmission through EIT

Shot Noise

Hetet et al. Opt Express 16 pp. 7369 (2008)10

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Shot Noise

Squeezing before EIT(~3.2dB)


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Shot Noise

Squeezing before EIT(~3.2dB)

Squeezing after EIT(~2dB)


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Delay of Entanglement through EIT


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Amplitude Phase


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Inseperability before EIT: 0.65±0.01

Amplitude Phase


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Inseperability before EIT: 0.65±0.01

Inseperability after EIT: 0.71±0.01

Amplitude Phase


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Overview

• Electromagnetically induced transparency (EIT)

• Delay of squeezed light & entanglement with EIT

• Photon echoes and the Gradient Echo Memory (GEM)

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Photon echoes

The art of inverting absorption

Excitation on a Bloch Sphere

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Photon echoes

The art of inverting absorption

Excitation on a Bloch Sphere Coherent re-emission?

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Photon echoes

Kurnit et al, Phys .Rev. Lett. 13, 567 (1964), T. W. Mossberg, Opt. Lett. 7, 77, (1982), C. Sjaarda Cornish et al. Opt Lett 25,1276 (2000)

Δ−Δ

Controlled Reversible Inhomogeneous broadening

Flipping an energy shift (eg Stark shift) reverses evolution of ensemble

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•Two levels and forward direction.•Linear spatial chirp of the atomic frequency

Gradient Echo Memory (GEM)

Hetet et al. Phys. Rev. Lett. 100 023601 (2008), Hétet et al., PRL 101, 203601 (2008).

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∂∂zE(z,t) = iNα(z,t)

Time domain

The GEM normal mode

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∂∂tα(z,t) = iη(t)zα(z,t) + igE(z,t)

Optical field

Atomic density

Atomic polarisation

Stark shift slope

G. Hétet et al., PRL 101, 203601 (2008)

Atom-light coupling

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∂∂zE(z,t) = iNα(z,t)

Time domain

The GEM normal mode

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∂∂tα(z,t) = iη(t)zα(z,t) + igE(z,t)

Optical field

Atomic density

Atomic polarisation

Stark shift slope

Spatial Fourier domain

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∂∂t−η(t) ∂

∂k+ iϕk

ψ(k, t) = 0

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ψ = a'(t)Ε + b'(t)α

F

Normal mode

Propagator

Like the EIT polariton, this a normal mode of light and

atoms, but now in k-space!G. Hétet et al., PRL 101, 203601 (2008)

Atom-light coupling

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Gaussian light pulse

Light

Atomic Polarisation

Normal mode

Evolution in space and time

G. Hétet et al., PRL 101, 203601 (2008).18

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k-space GEM normal mode shows temporal profile

Real-space EIT normal mode shows temporal profile

GEM and EIT normal modes

G. Hétet et al., PRL 101, 203601 (2008).19

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E-field

G. Hétet et al., PRL 101, 203601 (2008).20

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E-field

Time reversal of pulse

G. Hétet et al., PRL 101, 203601 (2008).20

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E-field

Atomic Polarisation


G. Hétet et al., PRL 101, 203601 (2008).20

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E-field

Atomic Polarisation

Pulse stored as Fourier transform


G. Hétet et al., PRL 101, 203601 (2008).20

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Modulated pulse storage movie

|E|

|α|

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Memory Efficiency ~ 15 %(Now up to 45%)

Experimental Results in a solid state system

Hetet et al. Phys. Rev. Lett. 100 023601 (2008)

Gradient Echo Memory (GEM)

Experiment by Longdell, Alexander and Sellars, RSPhysSE, ANU

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Ωc ( t )

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ˆ E (z,t)

3-level GEM

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•Previously, GEM used a 2-level optical transition.

•Raman coupling of a 3-level system can be used to form a quasi 2-level atom.

•The dynamics of the control beam are (in theory) unimportant.

•Ground states can be very long lived.

G. Hétet et al., Opt. Lett. 33, 2323 (2008)23

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3-level GEM protocol


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3-level GEM protocol

Detunedcontrol beam

As before but now the control beam is used to form 2-level atoms with coherence times of the ground states.

Detunedcontrol beam


Experiment with Rb vapour

ΩcE^

Coil design from Simon Bell, University of Melbourne

Experiment with Rb vapour

Zeeman gradient controlled using B-fields

ΩcE^

Coil design from Simon Bell, University of Melbourne

First observation of echo from Rb vapour

Efficiency is about 1%. G. Hétet et al., Opt. Lett. 33, 2323 (2008)

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Current best performance

Time (µs)

Inte

nsity

(ar

b.)

Switching Point

~7% echo efficiency

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Pulse mirroring

Echoes

Input pulses

Switching

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Pulse mirroring

Echoes

Input pulses

Switching

τstorage=15 μs

τstorage=25 μs

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Transition Between Raman and EIT

-0.5 0.0 0.5 1.0-1.00.0

0.2

0.4

0.6

0.8

1.0

Two photon detuning δ (MHz)

Nor

mal

ized

pro

be

tran

smis

sion Ωc

E

In the presence of Doppler broadening, some atoms are still close to resonance leading to control field induced decoherence.

Δ=0

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Transition Between Raman and EIT

-0.5 0.0 0.5 1.0-1.00.0

0.2

0.4

0.6

0.8

1.0

Two photon detuning δ (MHz)

Nor

mal

ized

pro

be

tran

smis

sion Ωc

Δ~1GHz

δ{Δ{

E

In the presence of Doppler broadening, some atoms are still close to resonance leading to control field induced decoherence.

Δ=0

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Inte

nsity

(ar

b)

Echoes

Input

Leakage

0.0 5.0 10.0 15.0 20.0 25.0

0

1

No control field during storage

Time (µs)

Control field induced decoherence

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Summary

EIT storage is a good option and already demonstrated.

GEM has some promising advantages - especially large bandwidth.

Future Directions:

Try difference hyperfine ground states

MOT?

Solid State?

More info, links to papers etc......

http://photonics.anu.edu.au/

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http://photonics.anu.edu.au

http://photonics.anu.edu.au

quantum memory with 3-level atoms - ifraf · arc centre of excellence for quantum atom optics the...

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