Decoherence issues for atoms in cavities & near surfaces Peter Knight, Imperial College London work with P K Rekdal,Stefan Scheel, Almut Beige, Jiannis Pachos, Ed Hinds and many others. Cold surfaces: cqed in bad and good cavity limits?
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Decoherence issues for atoms in cavities & near surfacesPeter Knight, Imperial College Londonwork withP K Rekdal,Stefan Scheel, Almut Beige, Jiannis Pachos, Ed Hinds and many others
Beige, Knight, Tregenna, Huelga, Plenio, Browne, Pachos…
how to live with noise, and use of decoherencefree subspaces
Slide from Tom Mossberg
Slide from Tom Mossberg
M.B. Plenio et al, Phys. Rev. A 59, 2468 (1999)
Cavity in vacuum state, with two atoms in their ground state.
Excite one atom!
Exchange of excitation between the atoms and the cavity mode.
No jump detection and Bell states
Entanglement between distant cavities.
S. Bose, P.L. Knight, M.B. Plenio and V. Vedral, PRL 58, 5158 (1999); Browne et al (2003/4)
D
+
Bob
D

Beam splitter destroys whichpath information!
A detected photon could have come from any cavity.
Alice
fluctuation of field
heating and spin flips
Spin flip lifetime above a thick slab/wire
height
spin flip
frequency
skin depth
metal slab
Henkel, Pötting and Wilkens Appl. Phys B 69,379 (1999);Scheel, Rekdal, PLK & Hinds
Warm surfaces: em field noise above a metal surface: Ed reprise
resistivity of metal
trapping light
BEC
Mott insulator
There can be exactly 1 atom per lattice site (number squeezing)
Ed’s vision: An atomic quantum registerintegrated fiber
Atom number distribution after a measurement
Superfluid LimitAtoms aredelocalized over the entire lattice!Macroscopic wave function describes this state very well.
Poissonian atom number distribution per lattice site
n=1
Atom number distribution after a measurement
Atomic Limit of a MottInsulatorAtoms are completely localized to lattice sites !
Fock states with a vanishing atom number fluctuation are formed.
n=1
D. Jaksch et al., PRL 82,1975(1999), G. Brennen et al., PRL 82, 1060 (1999)A. Sorensen et al., PRL 83, 2274 (1999)
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gb
ga
For U/J>11.6 approximately one atom per lattice site is obtained. For J=0 we obtain Fock states.
Mott insulator
Population
Sites
Use it as a register: one atom per site in a or b mode is a qubit in 0> or 1> state.
a
b
2
1
ga
gb
Exchange Interaction obtained. For J=0 we obtain Fock states.
11;00>
00;11>
01;10>
10;01>
J<<U
Exchange Interaction obtained. For J=0 we obtain Fock states.
11;00>
00;11>
01;10>
10;01>
J<<U
Quantum Computation obtained. For J=0 we obtain Fock states.
Gates obtained. For J=0 we obtain Fock states.
2. What about decoherence? obtained. For J=0 we obtain Fock states.
(A) Technical noise in the em field
Above currentcarrying wires
audiofrequency vibrates the trap heating
radiofrequency excites spin flips loss
In a fardetuned light trap
fluctuations of intensity, phase, polarization
heating and loss
In permanent magnet traps
We are just learning how to control technical noise in microtraps
time scale ~ 1100s
is there technical noise?