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Bingyang Zhang Yasuhiko Arakawa (Tokyo) Colin Stanley (Glasgow) Klaus Lischka (Paderborn)

Bingyang Zhang Yasuhiko Arakawa (Tokyo) Colin Stanley (Glasgow) Klaus Lischka (Paderborn) Kohei Ito (Keio) (MBE) Stephan G ötzinger Dirk Englund Shinichi Koseki David Press (Quantum dots). Kai-Mei Fu Susan Clark Kaoru Sanaka Alex Pawlis Charles Santori (HP) David Fattal (HP)

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Bingyang Zhang Yasuhiko Arakawa (Tokyo) Colin Stanley (Glasgow) Klaus Lischka (Paderborn)

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  1. Bingyang Zhang Yasuhiko Arakawa (Tokyo) Colin Stanley (Glasgow) Klaus Lischka (Paderborn) Kohei Ito (Keio) (MBE) Stephan Götzinger Dirk Englund Shinichi Koseki David Press (Quantum dots) Kai-Mei Fu Susan Clark Kaoru Sanaka Alex Pawlis Charles Santori (HP) David Fattal (HP) (Donor bound excitons) Thaddeus Ladd Fumiko Yamaguchi William Munro (HP) Kae Nemoto (NII) Peter van Loock (NII) (Quantum communication/ computation protocol) Jelena Vuckovic Yoshihisa Yamamoto The Forth International Symposium on Nanotechnology (Tokyo, Feb. 20-21, 2006) Is Clean Atomic Physics Implementedin Semiconductor Systems?— From Quantum Dots to Impurity Bound Excitons —

  2. Outline • Overview of the past work - Indistinguishable single photons from single QD microcavity - Quantum key distribution - Entangled photon-pairs (violation of Bell’s inequality) - Quantum teleportation - Limitation: What was the problem with QDs? • Substitutional donor impurities in semiconductors - Hydrogenic spectrum - Coherent population trapping (electron spins) - 1min coherence time (nuclear spins) • Cavity QED nodes connected by coherent state bus for photonic quantum information systems - Entanglement distribution - Non-local two qubit operation - Coherent emission and trapping of single photons

  3. level diagram: XX 2 - 4 meV X+ X- XH XV e- Cascade Photon Emission h+ empty 27 mW 108 mW 432 mW 1X time (ns) 3X 2X l (nm) l (nm) l (nm) Single QD Spectroscopy: “Artificial Atoms” • Sharp spectral lines • at low temperature • Multiparticle effects • Dephasing processes (~1nsec) (phonon,electrostatic) Above band excitation On resonant excitation at 2e-2h Suppression of X– and X+ lines Deterministic single photon generation Deterministic entangled photon-pair generation O. Benson et al., Phys. Rev. Lett. 84, 2513 (2000) C. Santori et al., Phys. Rev. Lett. 86, 1502 (2001)

  4. A. Imamoglu ( Zurich): Controlled placement of QD J.M.Gerard (CEA Grenoble) A. Forchel (Würzburg) Strong coupling A. Scherer (Cal. Tech) A. Shields (Toshiba Cambridge): Entangled photon-pair generation ECR (II) ECR (I) CAIBE M. Pelton et al., Phys. Rev. Lett. 89, 233602 (2002) G. Solomon et al., Phys. Rev. Lett. 86, 3903 (2001) J. Vuckovic et al., Appl. Phys. Lett. 82, 3596 (2003) Single QD Microcavities Photonic Crystal D. Englund et al., Phys. Rev. Lett. 95, 013904 (2005)

  5. + 1 2 { |1,rA;2,rB > |2,rA;1,rB> } rA 1 or 2? |y > = rB direct term exchange term symmetrization (Boson) anti-symmetrization (Fermion) Symmetrization postulate of Quantum Mechanics Probability of Two Particles in the Same Output Port rA = rB = r BOSON FERMION Quantum Indistinguishability Identical Quantum Particles Indistinguishable Suppressed due to Destructive Quantum Interference (Fermions) Enhanced due to Constructive Quantum Interference (Bosons) Pauli Exclusion Principle Final State Stimulation & BEC

  6. Hong-Ou-Mandel dip Indistinguishable Single Photons from a Single Quantum Dot— Measurement of Quantum Mechanical Overlap — C. Santori et al., Nature 419, 594 (2002) • Requirements: • Negligible jitter (2e-2h  1e-1h relaxation • time ~10 psec) compared to pulse duration • No phase jump (decoherence time ~2nsec) • in pulse duration

  7. Alice Counter Det 0 channel /2 plate Spec. slit He Cryo. /4 plate 50-50 BSP Pinhole PBS Sm fiber EOM Lens Lens Flip Mirror PBS Det 4 dot grating Laser Pulse Det 1 Det 3 Lens Det 2 TIA Amp. Data Gen. Bob TIA Communication rate 70KHz Error rate 3% E. Waks et al., Nature 420, 762 (2002) BB84 Quantum Key Distribution Experimentwith Single Photon Source Error correction Poissonian photon source Single photon source Privacy amplification

  8. HWP from QD a V H H A 1 2 b SPCM NPBS B Coincidence circuit = post-selection State tomography Generation of Entangled Photon-Pairs with Indistinguishable Single Photons and Linear Optics D. Fattal et al., PRL 92, 037903 (2004) • Input : • Output : Violation of Bell’s Inequality: a = 0/90oa’ = 45/135o b = 22.5/112.5ob’ = 67.5/157.5o SCHSH = 2.377± 0.18 > 2 • Entanglement is induced by the quantum indistinguishability: NO optical non-linearity required. • Ideal efficiency is ½. • Only single pairs are created. Ekert 91/BBM92 QKD Systems Mixed state due to g(2)(0)0 and V(0)<1.

  9. Single Mode Quantum Teleportation with Indistinguishable Single Photons D. Fattal et al., PRL 92, 037904 (2004) Finite visibility due to g(2)(0)0 and V(0)<1 Building block of linear/nonlinear optics quantum computation Massive parallel indistinguishable single photon sources (All QDs must have identical wavelength)

  10. Ｗｈａｔ　ｗａｓ　ｔｈｅ　ｐｒｏｂｌｅｍ　ｗｉｔｈ　ＱＤｓ?It is an “artificial atom” but not a “clean atom”.

  11. Atomic Physics in Semiconductor Systems– Donor Nuclear Spin, Bound Electron Spin (D0) and Exciton (D0X) System – EMT Envelope neutral donor bound exciton - L=3 2 electrons 1 hole D0X L=2 + L=0,1 - + Radiative excitation and recombination TES Main transition Quantum communication - neutral donor + 2s,2p D0 31P: Si 29Si: GaAs 19F: ZnSe 1 electron 1s electron spin -1/2 (quantum processor) simplest nuclear spin –½ (quantum memory) Background nuclear spins can be depleted for Si and ZnSe by isotope engineering

  12. Hydrogenic Spectrum of Impurity Bound Excitons in GaAs System Acceptor bound excitons in GaAs Donor bound excitons in GaAs Diamagnetic shift Zeeman splitting 1S R*y ionization energy: 25.9 meV Central cell corr.: > 3.8 meV Transition energy (meV) 2S 3S 4S 5S electron spin hole spin long T2 time short T2 time

  13. Enhancement due to optical pumping effect, T1 dip depth and width determine T2*, C Intensity, counts T2* = 1-3 ns T1 = 2.6 sec C* = 650 MHz P* = 16 MHz probe only Electromagnetically Induced Transparency (EIT)– Coherent Population Trapping Observed – K.M.Fu et al., Phys..Rev. Lett. 95, 187405 (2005) • Coherent trapping and release of optical pulses (or single photons) • Entanglement generation in remote nodes • Nonlinear interaction of photonic qubits

  14. Coherence Time T2 ~ 1 min for Nuclear Spins in Si T. Ladd et al., Phys. Rev. B. 71, 014401 (2005) natural linewidth fluctuating local magnetic field along Z-axis at dipolar coupling to other nuclear spins Spin echo CPMG  -pulse sequence decoupling ( -pulse sequence) Time (sec)

  15. detuning probe cavity 1. Initial states of two qubits 4. Homodyne measurement 2. Dispersive light-matter interaction (~0.01 : small phase shift) 3. Same interaction with qubit 2, followed by phase shift - post-selection Entanglement Distribution with Coherent State BusP. van Loock et al, quant-ph/0510202 (2005)

  16. Non-Local, Measurement-Free and Deterministic Two Qubit GateT. Spiller et al, quant. Ph/0509202 (2005) Time displacement (beamsplitter) controlled phase shift (reflection from cavity) • After the entire sequence, the probe is disentangled from the qubits. No measurement and post-selection required. • An overall phase develops proportional to area (topological phase), A desired phase shift of  achieved with

  17. 31P:Si – Optically Active in High Q Microcavity! • Lifetime-limited atomic linewidth: 3 MHz • via Auger recombination • Radiative lifetime: 2 ms • via phonon assisted process • Optimum regime for detuning is just off-resonance from atomic linewidth, but well inside bandwidth of cavity. • Q of 6  105 for silicon microcavity already observed at Kyoto Univ. and NTT-BRL

  18. control pulse (t) atom one-side microcavity 1. Deterministic single photon generation pulse duration 10 ps, quantum efficiency 99%, QM overlap 98%, no jitter, complete control of pulse amplitude coherent Rabi frequency (t) Vacuum Rabi frequency g0 2. Single photon detector with coherent state probe after trapping quantum efficiency 99%, no dark count, dead time 100 ps David Fattal, Ph.D thesis (Stanford University) Nonadiabatic Coherent Trapping and Emission of Arbitrary Single Photon Pulses

  19. Future Prospects A single donor impurity in semiconductor microcavity • Deterministic, indistinguishable single photon generation, trapping and release • High-speed and high-efficiency single photon detector with no dark count • Entanglement distribution by coherent state bus • Non-local deterministic two qubit gate by coherent state bus Ensemble of donor impurities in bulk semiconductor • Trapping and release of coherent optical pulse (or single photon) • Entanglement distribution by single photon detection Long distance quantum communication (connected by quantum repeater) Distributed quantum computation (connected by quantum teleportation network)

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