Quantum Information Processing with 10 10 Electrons? René Stock IQIS Seminar, October 2005 People: Barry Sanders Peter Marlin Jeremie Choquette
Motivation Quantum information processing realiations Ions Solid State systems NMR Photons Superconductors Neutral Atoms Need for hybridiation and interfacing of different technologies Surface Plasmons? coherent charge density oscillations involving 10 10 electrons
Outline What are surface plasmons: Introduction Excitation of surface plasmons at surfaces Entanglement and surface plasmons Surface plasmons in quantum information implementations
Outline What are surface plasmons: Introduction Excitation of surface plasmons at surfaces Entanglement and surface plasmons Surface plasmons in quantum information implementations
What are surface plasmons? Electric field propagating at surface E r x metal dielectric + + + + + + H y Maxwell Equations and continuity D = ε 0 E + P = εe (linear medium) ε 2 E x1 E 1 = 0 exp i k x k ωt x1 1 E 1 [ ( )] 0 H 1 = E y1 exp i k x k ωt x1 1 0 [ ( )] E x 2 E 2 = 0 exp i k x + k ωt x 2 2 E 2 [ ( )] 0 H 2 = E y 2 exp i k x + k ωt x 2 2 0 [ ( )] divd = 0 E x1 = E 1 = E x 2 ε 2 E 2 SP Dispersion relation rot H 1 c divb = 0 D t = 0 H y1 = k 1 H y1 = k x = ω ε 2 H y2 c + ε 2 k 2 H y2 ε 2 ω 2 k 2 x + k 2 i = ε i c 2
What are surface plasmons? Evanescent electric E r field propagating at surface E e k x metal dielectric + + + + + + H y ε 2 E Surface Plasmon: Longitudinal charge density oscillations involving 10 10 electrons k sp = ω c ε 2 + ε 2 Surface Plasmon Polariton: Polaritons are quasiparticles resulting from strong coupling of electromagnetic waves with an electric or magnetic dipolecarrying excitation, in this case plasmons.
What are surface plasmons? Evanescent electric E r field propagating at surface E e k x metal dielectric + + + + + + H y ε 2 E k x = ω c e.g. ε 2 + ε 2 Ag Au ε = 22.4 0.91i ε = 23.0 0.77i = + i ε 2 is real < [ also ε( ω) ] k x = ω c k x = ω c ε 2 + ε 2 ε 2 + ε 2 1 2 3 2 ε 1 2 ( ) 2
What are surface plasmons? Evanescent electric E r field propagating at surface E e k x metal dielectric + + + + + + H y ε 2 δ m δ d E [Figures courtesy of Barnes et al., Nature 424, p824 (2003)] δ sp k x = ω c ε 2 + ε 2 3 2 2 ( ) 2 Extremely short lifetimes for surface plasmons ( 10-15 s to 10-12 s)
Outline What are surface plasmons: Introduction Excitation of surface plasmons at surfaces Entanglement and surface plasmons Surface plasmons in quantum information implementations
Attenuated total reflection Excitation of Surface Plasmons k sp = ω c k x = sinθ ε 0 ω c r k light ε 2 + ε 2 < ω c [Figures courtesy of Barnes et al., Nature 424, p824 (2003)] r k x r k sp θ res metal film attenuated total reflection at surface plasmon resonance [other figures courtesy of R. Stock, Thesis, UNM (2001)]
Excitation of Surface Plasmons Attenuated total reflection 0.4 0.3 prism gold air k sp = ω c ε 2 + ε 2 < ω c E ( ) 2 E 0 0.2 normal incidence 0.1 k x = sinθ ε 0 ω c r k light r k x r k sp θ res metal film E ( ) 2 E 0 0-200 0 200 400 600 0-200 0 200 400 600 strong field enhancement effect due to surface plasmons [Figures courtesy of R. Stock, Thesis, UNM (2001)] 8 7 6 5 4 3 2 1 distance (Å) prism gold air surface plasmon resonance angle
Periodic structure r k sp = k r x ± mg r x ± ng r y m 2 + n 2 λ = D ε 2 + ε 2 Periodic sub wavelength hole array Excitation of Surface Plasmons versatile wavevector matching using periodic structures [Figures courtesy of Ghaemi et al., PRB 58, p6779 (1998) and Altewischer et al., Nature 418, p304 (2002)]
Periodic sub wavelength hole array Excitation of Surface Plasmons 700 nm 200 nm k sp k sp 200 nm Enhanced optical transmission through array of sub wavelength holes (compared to diffraction theory) [Figures courtesy of Ghaemi et al., PRB 58, p6779 (1998) and Altewischer et al., Nature 418, p304 (2002)]
Outline What are surface plasmons: Introduction Excitation of surface plasmons at surfaces Entanglement and surface plasmons Surface plasmons in quantum information implementations
Implementations using Surface Plasmons Field enhancement effect Surface enhanced spectroscopy Strong coupling to waveguides Biophotonics: Biological and chemical detectors (sensitivity to ε 2 at the surface) Nanoscale technology Nano-optics and nano-circuitry on surfaces: Mirrors (reflectivity> 90%) Nanowires (waveguides) for plasmons Plasmonic computer chips and other nanoscale technology Data storage Quantum nature of surface plasmons SPASERS (surface plasmon amplification by spontaneous emission of radiation) Single photon light sources Quantum information processing Seidel et al., PRL 94, 177401 (2005)
Polariation entangled photons Surface Plasmons and Entanglement ψ = 1 ( 2 X Y 1 2 + e iφ Y 1 X 2 ) Experimental setup Nature 418, p304 (2002) Coincidence detection after transmission through hole array
Surface Plasmons and Entanglement Experiment Reduced visibility due which-path information in solid?
Surface Plasmons and Entanglement Which-path information: include state of solid E. Moreno, F.J. Garcia-Vidal, D. Erni, J. I. Cirac, L. Martin-Moreno PRL 92, 236801(2004) Interaction models? S ab a) all are orthogonal: solid and biphoton entangled trace over solid: mixed state for biphoton, which-polariation information b) all S ab are equal: no entanglement between solid and photon states trace over solid: biphoton entangled depending on t ab Choose b): no which-path labels introduced in solid Observed visibilities can be explained by polariation dependent transmission of hole array
Surface Plasmons and Entanglement Energy-time entanglement S. Fasel, N. Gisin, H. Zbinden, D. Erni, E. Moreno, F. Robin PRL 94, 110501(2005) ψ = 1 ( 2 1,0;1,0 + AB eiφ 0,1;0,1 AB ) energy-time entanglement especially robust against environmental disturbance telecom wavelength particularly interesting for quantum communication
Surface Plasmons and Entanglement Energy-time entanglement S. Fasel, N. Gisin, H. Zbinden, D. Erni, E. Moreno, F. Robin PRL 94, 110501(2005) macroscopic cat states (surface plasmons) living at different epochs that differ by more than the cats (surface plasmon) lifetime
Outline What are surface plasmons: Introduction Excitation of surface plasmons at surfaces Entanglement and surface plasmons Surface plasmons in quantum information implementations
Surface Plasmons in Quantum Information Proposal: Cavity QED with Surface Plasmons D. E. Chang, A. S. Sorensen, P. R. Hemmer, and M. D. Lukin quant-ph/0506117 efficient coupling of emitter (quantum dot, atom) to plasmon mode of nanowire evanescent coupling of nanowire to dielectric waveguide single photon source plasmon cavity created by plasmon mirrors (2k grating on surface) with reflectivity > 0.9 field enhancement: stronger coupling and faster interaction times one photon sources
Surface Plasmons in Quantum Information Proposal: Cavity QED with Surface Plasmons D. E. Chang, A. S. Sorensen, P. R. Hemmer, and M. D. Lukin quant-ph/0506117 calculation of plasmons modes efficiency of single photon generation P fractional power emitted into fundamental plasmon mode one photon source efficiency: 0.7 (coupling to wire), 0.9 coupling to cavity
Summary Summary Entanglement survives excitation and deexcitation of surface plasmons Applications for hybridiation of different QIP implementations Problems: Short Coherence time (usually < 10-12 s) Limited spatial propagation (usually < 1 mm) References General review: Surface Plasmons: Entanglement experiments Theoretical analysis Time-energy entanglement Hybrid proposal J. Opt. A 5, S16-S50 (2003) H. Raether: Surface Plasmons, Springer 1988 Nature 418, 304 (2002) PRL 92, 236801(2004) PRL 94, 110501(2005) quant-ph/0506117