Quantum mechanical wonders

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Quantum Memory for Light
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Quantum memory for light criteria

• Memory must be able to store independently
  prepared
• states of light

• The state of light must be mapped onto the
  memory with
• the fidelity higher than the fidelity of the
  best
• classical recording

• The memory must be readable

B. Julsgaard, J. Sherson, J. Fiuráek , I. Cirac,
and E. S. Polzik Nature, 432, 482 (2004)
quant-ph/0410072.
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These criteria should be met for memory in
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Mapping a Quantum State of Light onto Atomic
Ensemble
The beginning. Complete absorption
Squeezed Light pulse
Proposal Kuzmich, Mølmer, EP PRL 79, 4782
(1997)
Atoms
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Our light-atoms interface - the basics
Light pulse consisting of two modes
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Teleportation in the X,P representation
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Today another idea for (remote) state
transfer and its experimental implementation for
quantum memory for light
See also work on quantum cloning J. Fiurasek, N.
Cerf, and E.S. Polzik, Phys.Rev.Lett. 93,
180501 (2004)
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Implementation light-to-matter state transfer
No prior entanglement necessary
C
Feedback magnetic coils
Cesium atoms
F80
F?100
B. Julsgaard, J. Sherson, J. Fiuráek , I. Cirac,
and E. S. Polzik Nature, 432, 482 (2004)
quant-ph/0410072.
9
Classical benchmark fidelity for transfer of
coherent states
Atoms
Best classical fidelity 50
K. Hammerer, M.M. Wolf, E.S. Polzik, J.I. Cirac,
Phys. Rev. Lett. 94,150503 (2005),
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Preparation of the input state of light
Strong field A(t)
Quantum field - X,P
x
Polarizing cube
S1
P
Polarization state
X
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Quantum memory Step 1 - interaction
Light rotates atomic spin Stark shift
XL
Atomic spin rotates polarization of light
Faraday effect
Output light
Input light
Entanglement
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Quantum memory Step 2 - measurement feedback
Polarization measurement
Fidelity gt 100 (82 without SS atoms)
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Experimental realization of quantum memory for
light
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Encoding the quantum states in frequency sidebands
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Memory in atomic Zeeman coherences
Cesium
4
3
2
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Memory in rotating spin states
y
z
Atomic Quantum Noise
2,4
2,2
2,0
1,8
1,6
1,4
1,2
Atomic noise power arb. units
1,0
0,8
0,6
0,4
0,2
0,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Atomic density arb. units
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Memory in rotating spin states - continued
x
z
y
Atomic Quantum Noise
2,4
2,2
2,0
1,8
1,6
1,4
1,2
Atomic noise power arb. units
1,0
0,8
0,6
0,4
0,2
0,0
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
Atomic density arb. units
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x
z
y
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Stored state versus Input state mean amplitudes
X plane
read
write
t
output
input
Y plane
Magnetic feedback
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Stored state variances
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Fidelity of quantum storage

• State overlap averaged over
• the set of input states

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Quantum memory lifetime
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Quantum Memory for Light demonstrated

• Deterministic Atomic Quantum Memory proposed and
• demonstrated for coherent states with ltngt in
• the range 0 to 10 lifetime4msec

• Fidelity up to 70, markedly higher than best
• classical mapping