Session A1: Silicon Qubits

Coherent control of donor states in Si

The spin degrees of freedom of group V donors in Si satisfy many of the criteria required for qubits [1,2]. The orbital Rydberg states of group V donors can also be used to control these spins coherently [3,4]. Critical to such schemes are the population (T$_{1})$ and dephasing (T$_{2})$ lifetimes of these Rydberg states. We describe the use the free electron laser FELIX [5] to perform pump-probe experiments to measure T$_{1}$ [6] and photon echo experiments to measure T$_{2}$ [7]. The lifetimes we obtain from a theoretical analysis of the experiments are $\sim $ 200 ps, which is long enough for orbital excitation to be a practical control mechanism for 2-qubit quantum gates. The experimental and theoretical analysis of these gates is also described. \\[4pt] [1] DiVincenzo D P, ``The Physical Implementation of Quantum Computation,'' arXiv:quant-ph/0002077 \\[0pt] [2] Morley G W, \textit{et al}, ``Initializing, manipulating and storing quantum information with bismuth dopants in silicon'' \textit{ Nature Materials} \textbf{9} 725 -- 729 (2010) (doi:10.1038/nmat2828) \\[0pt] [3] Stoneham, A. M., Fisher, A. J. {\&} Greenland, P.T. ``Optically driven silicon-based quantum gates with potential for high-temperature operation'' \textit{ J Phys Condens Matter} \textbf{15}, L447-451 (2003). \\[0pt] [4] http://arxiv.org/find/cond-mat/1/au:+Wu\_W/0/1/0/all/0/1 Wu W, Greenland P T, Fisher A J, ``Exchange in multi-defect semiconductor clusters: assessment of `control-qubit' architectures'' http://arxiv.org/abs/0711.0084 \\[0pt] [5] Knippels G M H, \textit{et al}, ``Generation and Complete Electric-Field Characterization of Intense Ultrashort Tunable Far-Infrared Laser Pulses'' \textit{ Phys. Rev. Lett}. \textbf{83}, 1578-1581 (1999) \\[0pt] [6] N Q Vinh N Q et al, ``Silicon as a model ion trap: time domain measurements of donor Rydberg states'' \textit{PNAS} 105 10649-10653 (2008) \\[0pt] [7] Greenland P T et al \textit{Nature}, 465, 1057-1061 (2010) (doi:10.1038/nature09112)   

Single-shot readout and microwave control of an electron spin in silicon

The electron spin of a donor in silicon is an excellent candidate for a solid-state qubit. It is known to have very long coherence and relaxation times in bulk [1], and several architectures have been proposed to integrate donor spin qubits with classical silicon microelectronics [2]. Here we show the first experimental proof of single-shot readout of an electron spin in silicon. The device consists of implanted phosphorus donors, tunnel-coupled to a silicon Single-Electron Transistor (SET), where the SET island is used as a reservoir for spin-to-charge conversion [3]. The large charge transfer signals allow readout fidelity $>90${\%} with 3 $\mu $s response time. By measuring the occurrence of excited spin states as a function of wait time, we find spin lifetimes $(T_{1})$ up to $\sim $~6 s at $B = 1.5$~T, and a magnetic-field dependence $T_{1}^{-1} \propto B^{5}$ consistent with that of phosphorus donors in silicon [4]. In a subsequent experiment we have integrated the single-shot spin readout device with an on-chip microwave transmission line for coherent control of the electron spin. We have detected the spin resonance of a single electron, and observed two hyperfine-split resonance lines, consistent with Stark-shifted coupling to the $^{31}$P nuclear spin. Further experiments are underway to demonstrate coherent spin control and observe Rabi oscillations. This demonstrates the microwave control of a single spin, combined -- for the first time in the same experiment -- with electrically detected single-shot spin readout. \newline [1] A. M. Tyryshkin \textit{et al}., Phys. Rev. B \textbf{68}, 193207 (2003). \newline [2] L. C. L. Hollenberg \textit{et al}., Phys. Rev. B. \textbf{74}, 045311 (2006). \newline [3] A. Morello \textit{et al}., Phys. Rev. B \textbf {80}, 081307(R) (2009). \newline [4] A. Morello \textit{et al}., Nature \textbf{467}, 687 (2010).   

Integrated Quantum Photonics

Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [3]), measurement (eg. [4]) and other quantum technologies [5]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturisation and scalability [6]. Here we report high-fidelity silica-on-silicon integrated optical realisations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [7]. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [8]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [9] and demonstrated heralded generation of tuneable four photon entangled states from a six photon input [10]. We have combined waveguide photonic circuits with superconducting single photon detectors [11]. Finally, we describe complex quantum interference behaviour in multi-mode inter- ference devices with up to eight inputs and outputs [12], and quantumwalks of correlated particles in arrays of coupled waveguides [13].\\[4pt] [1] T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe, and J. L. OBrien, Nature 464, 45 (2010).\\[0pt] [2] J. L. O'Brien, Science 318, 1567 (2007).\\[0pt] [3] T. Nagata, R. Okamoto, J. L. O'Brien, K. Sasaki, and S. Takeuchi, Science 316, 726 (2007).\\[0pt] [4] R. Okamoto, J. L. O'Brien, H. F. Hofmann, T. Nagata, K. Sasaki, and S. Takeuchi, Science 323, 483 (2009).\\[0pt] [5] J.L.O'Brien,A.Furusawa, and J.Vuckovic, NaturePho- ton. 3, 687 (2009).\\[0pt] [6] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O'Brien, Science 320, 646 (2008).\\[0pt] [7] A. Laing, A. Peruzzo, A. Politi, M. R. Verde, M. Halder, T. C. Ralph, M. G. Thompson, and J. L. O'Brien, arXiv:1004.0326\\[0pt] [8] J. C. F. Matthews, A. Politi, A. Stefanov, and J. L. O'Brien, Nature Photon. 3, 346 (2009).\\[0pt] [9] A. Politi, J. C. F. Matthews, and J. L. O'Brien, Science 325, 1221 (2009).\\[0pt] [10] J. C. F. Matthews, A. Peruzzo, D. Bonneau, and J. L. O'Brien, arXiv:1005.5119\\[0pt] [11] C. M. Natarajan, A. Peruzzo, S. Miki, M. Sasaki, Z. Wang, B. Baek, S. Nam, R. H. Hadfield, and J. L. O'Brien, Appl. Phys. Lett. 96, 211101 (2010).\\[0pt] [12] A. Peruzzo, A. Laing, A. Politi, T. Rudolph, and J. L. O'Brien, arXiv:1005.5119\\[0pt] [13] A. Peruzzo, M. Lobino, J. C. F. Matthews, N. Matsuda, A. Politi, K. Poulios, X.-Q. Zhou, Y. Lahini, N. Ismail, K. Worhoff, Y. Bromberg, Y. Silberberg, M. G. Thompson, and J. L. O'Brien, Science 329, 1500 (2009)   

The initialization and manipulation of quantum information stored in silicon by bismuth dopants

This abstract not available.