Decoherence issues for atoms in cavities & near surfaces
Download
1 / 54

Cold surfaces: cqed in bad and good cavity limits? - PowerPoint PPT Presentation


  • 61 Views
  • Uploaded on

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?

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Cold surfaces: cqed in bad and good cavity limits?' - magar


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

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

  • Cold surfaces: cqed in bad and good cavity limits?

  • Warm surfaces & cold atoms: Atom chips, Mott transition & registers and spin flips


height

Cold surface

Mirror qed

Dielectric layer

Multilayer

PBG

JCM limit



Cavities
cavities

  • Barton Proc Roy Soc 1971

  • Milonni & Knight, 1973

  • Kleppner

  • Hinds, Haroche, Mossberg,

  • Kimble

  • And now with ions in Innsbruck and Munich


Dielectric output coupler
Dielectric output coupler

  • Dutra & Knight, Optics Commun 117, 256, 1995; Phys Rev A53, 3587, (1996);

  • Neat Bessel beam output for microcavity



Beige, Knight, Tregenna, Huelga, Plenio, Browne, Pachos…

how to live with noise, and use of decoherence-free subspaces


Cqed good cavity fundamentals
Cqed good cavity fundamentals

Slide from Tom Mossberg


Cqed fundamentals
Cqed fundamentals

Slide from Tom Mossberg


Two atoms in a cavity entanglement via decay
Two atoms in a cavity: entanglement via decay

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 which-path information!

A detected photon could have come from any cavity.

Alice


Cold atoms and warm surfaces
Cold atoms and warm surfaces

  • Atom chip guides: Ed’s talk

  • Atom registers made via Mott Transition from BEC

  • Addressing & gates

  • Heating and decoherence


dissipation in surface

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


Ed s vision an atomic quantum register

electrostatic wires

trapping light

BEC

Mott insulator

There can be exactly 1 atom per lattice site (number squeezing)

Ed’s vision: An atomic quantum register

integrated fiber



Superfluid limit

Atom number distribution after a measurement

Superfluid Limit

Atoms aredelocalized over the entire lattice!Macroscopic wave function describes this state very well.

Poissonian atom number distribution per lattice site

n=1


Atomic limit of a mott insulator

Atom number distribution after a measurement

Atomic Limit of a Mott-Insulator

Atoms are completely localized to lattice sites !

Fock states with a vanishing atom number fluctuation are formed.

n=1


Quantum gates with neutral atoms
Quantum gates with neutral atoms

  • Bring atoms into a superposition of internal states

  • Move atoms state selectively to neighbouring site

  • Interaction phase (Collisions or Dipole-Dipole)

  • Create large scale entanglement

  • Ising model

  • Hamiltonian simulations

  • Multi-particle interferometer

D. Jaksch et al., PRL 82,1975(1999), G. Brennen et al., PRL 82, 1060 (1999)A. Sorensen et al., PRL 83, 2274 (1999)


Optical lattices mott register physical system
Optical Lattices Mott Register Physical System

e

  • Raman transition:

  • Optical lattice model

  • Tunnelling transitions (J) and collisions (U)

  • Hamiltonian:

gb

ga


PHASE TRANSITION

8 atoms in 10 sites

Superfluid phase

Population

Sites

In harmonic potential V~U


Superfluid phase

Population

Sites


Mott insulator

Population

Sites


Mott insulator

Population

Sites


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.


Coherent interactions
Coherent Interactions obtained. For J=0 we obtain Fock states.

  • Consider the occupational state of two lattice sites:

a

b

2

1

  • Atomic Raman trans.

  • a b

ga

gb

  • Tunnelling trans.

  • 1 2


Exchange Interaction obtained. For J=0 we obtain Fock states.

  • Consider the evolution of the state |01;10> and |10;01> when we lower the potential of both a and b-modes. They are coupled to |00;11> and |11;00> by

|11;00>

|00;11>

|01;10>

|10;01>

  • Evolution: effective exchange interaction

  • Heff =-K(|10><01|+|01><10|)

J<<U


Exchange Interaction obtained. For J=0 we obtain Fock states.

  • Consider the evolution of the state |01;10> and |10;01> when we lower the potential of both a and b-modes. They are coupled to |00;11> and |11;00> by

|11;00>

|00;11>

|01;10>

|10;01>

  • Evolution: effective exchange interaction

  • Heff =-K(|10><01|+|01><10|)

J<<U


Quantum Computation obtained. For J=0 we obtain Fock states.

  • One qubit gate by Raman transitions between the states |0>=|ga > and |1 >=|gb >.

  • Two qubit gates by modulations of lattice potential

    • Conditional Phase gate: |11> |11>

    • : |01> (|01>+i|10>)


Gates obtained. For J=0 we obtain Fock states.

  • “Charge based” quantum computation with Optical Lattice.

  • Mott Insulator of 1 atom/site serves as a register. Two in-phase lattices trap two ground states of the atom [logical |0> and |1>].

  • One qubit gates by Raman transitions |0> |1>.

  • Two qubit gates [control phase-gates or ] performed by exchange interactions in one or both of the optical lattices, respectively.

  • Can perform multi-qubit gates in one go.


2. What about decoherence? obtained. For J=0 we obtain Fock states.

(A) Technical noise in the em field

Above current-carrying wires

audiofrequency vibrates the trap heating

radiofrequency excites spin flips loss

In a far-detuned 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 ~ 1-100s

is there technical noise?



Basic idea
Basic idea (2004)


Numerical results
Numerical results (2004)

  • Copper core, radius a1 185 microns plus 55 micron radius a2 Al layer

  • Use quoted resistivities to get skin depths delta of 85 microns for Cu and 110 microns for Al at frequency 560 kHz used by Ed’s group

  • One conclusion: Ed is a bit more wiry than slabby…


Conclusions
conclusions (2004)

  • Quantum information with optical lattices and atom chips has great potential

  • Quantum optics techniques on atom chips can probably make basic gates

  • Decoherence is an interesting problem: heating rates of seconds gives loads of time for gates.

  • Quantum memories are harder to realize: few qubit applications?

  • Funding:


  • ad