A. ImamogluDepartment of Electrical and Computer Engineering, and

Department of Physics,University of California, Santa Barbara, CA 93106

 

Quantum Dot Single-Photon Source: Prospects for Applications in Quantum Information Processing

Outline1) Quantum dots2) Properties of quantum dot single photon sources3) High efficiency photon counters

Co-workersA. Kiraz, J. Urayama, B. Gayral, C. Becher, P. Michler,

C. Reese, L. Zhang, E. HuW.Schoenfeld, B. Gerardot, P. Petroff

Requirements for linear optics quantum computation (LOQC)

• Linear optical elements: beam-splitters, polarizers, lenses optical delay/memory

• Single-photon sources: indistinguishable single-photon pulses on demand (with efficiency > 99%)

• Photon counters: high-efficiency detectors with single-photon discrimination

Appears to avoid the very demanding requirement for large (coherent) photon-photon interactions.

Single Photon SourcesSingle Photon Sources

Single atom in a cavity:Rempe et al. PRL (2002)

Single nitrogen vacancy in diamond:H. Weinfurter et al. PRL (2000)P. Grangier et al. PRL (2002)

Single Molecule at room temperature:B. Lounis and W.E. Moerner, Nature (2000)

Single InAs Quantum Dot in a microcavity:P. Michler et al., Science 290, 2282 (2000)C. Santori et al., PRL 86, 1502 (2001)Z. Yuan et al., Science 295, 102 (2002)

A regulated sequence of optical pulses that contain one-and-only-one photon

What is the signature of a single-photon source?

2)2(

)(

:)()(:)(

tI

tItIg

• Intensity (photon) correlation function:

gives the likelihood of a second photon detection event at time t+, given an initial one at time t ().

What is the signature of a single-photon source?

2)2(

)(

:)()(:)(

tI

tItIg

• Intensity (photon) correlation function:

• Experimental set-up for photon correlation [g(2)()] measurement:

Records the waiting-time between the successive photon-detection events at the two detectors (APD).

gives the likelihood of a second photon detection event at time t+, given an initial one at time t ().

Signature of a triggered single-photon source

• Triggered single photon source: absence of a peak at =0 indicates that none of the pulses contain more than 1 photon.

Signature of a triggered single-photon source

2)2(

)(

:)()(:)(

tI

tItIg

• Intensity (photon) correlation function:

gives the likelihood of a second photon detection event at time t+, given an initial one at time t ().

g(2)

0

Quantum Dots

• Artificial structures that confine electrons (and holes) in all 3 dimensions.

Atoms Quantum dots (QD)

Quantized (discrete) eigenstates in both cases ( 0D density of states).

Vatom (x) VQD (x) EQDEatom

Å Å

Eatom~ 1–10 eV >> kTroom = 26 meV

EQD ~ 1–100 meV ~ kTroom !

Unlike atoms, QDs are sensitive to thermal fluctuations at room temp.

Quantum Dots vs. Atoms

• Strongly trapped emitters: QDs do not have random thermal motion.

• Easy integration in nano-cavity structures.

• Strong coupling to optical fields: QD oscillator strength

f ~ 10 – 300 (collective enhancement).

• Electrical injection of carriers (electrons and holes).

• Each QD has a different resonance (exciton) energy.

• Difficult to tune QDs into resonance with cavity modes.

Self-Assembled InAs Quantum Dots

Atom-like characteristics of Quantum Dots:• sharp emission lines • photon antibunching

artificial atom for T < 77 K!