Slide 1

Generation of triggered single photons from Generation of triggered single photons from a coherently pumped quantum dota coherently pumped quantum dot

P. K. P. K. PathakPathak

Department of PhysicsQueen’s University,Kingston, ON, Canada

Slide 2

Single photon sourceSingle photon source

1.

Quantum cryptographyN. Gisin, et al, RMP 74, 145 (2002)

2. Quantum computationE. Knill, et al, Nature 409, 46 (2001)P. Kok, et al, RMP 79, 135 (2007).

3. Quantum NetworkingC. Monroe, Nature 416, 238 (2002).

Stringent requirements:1-

high indistingushability

Wavepacket, frequency, phase

2-

deterministic

: very high efficiency

Quantum correlations

50/50 BS

1

1

111 2,0 0,22

pulse

photon

Slide 3

Efficient channelling of emitted photons from QDs

has beenachieved by coupling with a waveguide or a cavity mode.

1. Atom trapped in optical cavityG. Rempe

group, Nat. Phys. 3, 253 (2007)

2. Ion trap

Kurtsiefer

et al., PRL 85, 290 (2000) 3. Single nitrogen-vacancy center in diamond

Keller et al., Nature 431

1075 (2004).

4. Quantum Dot micro-cavityC. Santori, et al. Nature 419, 594 (2002).

Excitation of QDs

was possible incoherently till now!!

SPS → Excitation mechanism Channelling

of photons

Excitation coherent or Incoherent

pumpemission

Slide 4

QD Source of Single photonsQD Source of Single photons

Incoherent pumped sourceIncoherent pumped source

cavity

Collection efficiency

Indistinguishability

= 1-P

Probability of coincidence detection

Kiraz

et al, PRA 69, 032305 (2004)

Purcell factor

1

1

Indistinguishability

= 1-PIndistinguishability

= 1-P

Coincidence detection

Slide 5

Dependence of collection efficiency and Dependence of collection efficiency and indistinguishabilityindistinguishability

For pi-pulse excitation

Kiraz

et al, PRA 69, 032305 (2004)

Slide 6

Coherent excitationCoherent excitation

0 0( ) 2

20 0

p

p s

s

H t

( ) sin ( )cos ( ) sin ( ) cos ( )cos ( )t g t t u t e t t

( ) sin ( )sin ( ) cos ( ) sin ( )cos ( )t g t t u t e t t

( )tan ( )

( )p

s

tt

t

2 2( ) ( )tan 2 ( ) p st t

t

dark state0 ( ) cos ( ) sin ( )t g t e t

Hamiltonian

Dressed state

STIRAPSTIRAP

Pi-pulsesnot robust against fluctuationsfast, efficient in two level system

Slide 7

Adiabatic evolution

Highly efficient population transferHighly efficient population transfer

0 ( ) cos ( ) sin ( )t g t e t dark state

( )tan ( )

( )p

s

tt

t

Counterintuitive order of pulses

intermediate

t

Slow varying pulse

Slide 8

AutlerAutler--townestownes

splitting in QD splitting in QD

Single photon source:Single photon source:

atom-cavity system

B. D. Gerardot

et al., New J. Phys. 11, 013028 (2009).

Rempe

group, Appl. Phys. B 69, 373 (1999)

QD

Slide 9

g,Cavity

Coherent pumped Single photons sourceCoherent pumped Single photons source

pump

cw

laser

STIR

AP

Dressed state

Slide 10

Micro-pillar

Suitable experimental systemsSuitable experimental systems

Planer cavity

photonphoton

Cw

laser+

PulseCw

laser+

Pulse

Slide 11

Hamiltonian of the system

Master equation

radiative

decay

cavity mode leakage

dephasing

g,Cavity

Slide 12

Populations in QDPopulations in QD--levels for two pulseslevels for two pulses

Pump pulse

Slide 13

Indistinguishability=1-P more than 90%

Second order correlation and Second order correlation and indishtinguishabilityindishtinguishability

Collection efficiency

nearly 100%

Probability of coincidence counts

//

//1

1

Slide 14

Dependence of Dependence of indishtinguishabilityindishtinguishability

on on dephasingdephasing

Slide 15

Summary Summary

•

Possibility of STIRAP in QD biexciton-excitoncascade.

•

Scheme for coherent pumped single photon source.

•

Arbitrarily large indistigushability

and collection efficiency can be achieved using STIRAP.

•

Thank YouThank You