Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session A36: Focus Session: Semiconductor Qubits: Optically Addressed Impurities & Quantum Dots |
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Sponsoring Units: GQI Chair: Sophia Economou, Naval Research Laboratory Room: 703 |
Monday, March 3, 2014 8:00AM - 8:12AM |
A36.00001: Cavity QED in a Quantum Dot Molecule Coupled to a Photonic Crystal Cavity Patrick Vora, Samuel Carter, Chul Soo Kim, Mijin Kim, Timothy Sweeney, Lily Yang, Peter Brereton, Allan Bracker, Daniel Gammon Semiconductor quantum dots (QDs) are a promising system for quantum information. InAs QDs grown within a GaAs diode heterostructure can be charged with a single electron, thereby serving as a spin qubit, and can easily be integrated with photonic circuits. An alternative qubit is the quantum dot molecule (QDM), a pair of QDs separated by a tunnel barrier. QDMs can be charged with two electrons that form spin singlet and triplet ground states which are less susceptible to nuclear spin effects. Furthermore, QDMs allow radiative recombination between carriers localized on different QDs. These interdot transitions can be tuned over a large range with applied voltage making them attractive as single photon sources. We have demonstrated coupling between a QDM and a two-dimensional photonic crystal cavity. A number of novel cavity-QED phenomena have been observed such as Purcell enhancement of interdot transitions, cavity-assisted Raman scattering, Autler-Townes splitting, and a cavity-induced AC Stark effect in a solid state $\Lambda$ system. These results have important implications for highly tunable single photon sources and also the development of a quantum network within a photonic crystal structure. [Preview Abstract] |
Monday, March 3, 2014 8:12AM - 8:24AM |
A36.00002: Complete quantum control of an exciton qubit bound to an isoelectronic center in GaAs Gabriel Ethier-Majcher, Philippe St-Jean, Gianluca Boso, Alberto Tosi, Sebastien Francoeur Various schemes of quantum information processing rely on interconnection of matter qubits via optical photons, flying qubits. To achieve scalable and robust quantum computing and networking within those schemes, matter qubits must present high optical homogeneity and strong coupling to photons. Here, coherent optical manipulation of excitons bound to single isoelectronic centers formed from a pair of nitrogen isovalent impurities in GaAs is demonstrated. Using a time-gated technique, resonant fluorescence of the exciton is measured and the power dependence of the fluorescence shows Rabi rotations from which a dipole moment as high as 55 D can be extracted. Interestingly, excitation induced dephasing, a phenomenon lowering the fidelity of exciton gating in quantum dots, is strongly reduced in our system. The complete quantum control of the qubit is demonstrated through Ramsey interferometry. The coherence time of the exciton reaches 115 ps. Our results show that isoelectronic centers combine the strong dipole moments of quantum dots and the optical homogeneity and predictability of atomic systems such as NV centers in diamond, establishing them as promising candidates for quantum information processing. [Preview Abstract] |
Monday, March 3, 2014 8:24AM - 8:36AM |
A36.00003: Universal control and error correction in multi-qubit spin registers in diamond Tim Hugo Taminiau, Julia Cramer, Toeno van der Sar, Viatcheslav V. Dobrovitski, Ronald Hanson Quantum registers of nuclear spins coupled to electron spins of individual solid-state defects are a promising platform for quantum information processing. Pioneering experiments selected defects with favourably located nuclear spins having particularly strong hyperfine couplings. For progress towards large-scale applications, larger and deterministically available nuclear registers are highly desirable. Here we present universal control over multi-qubit spin registers by harnessing abundant weakly coupled nuclear spins [1,2]. We use the electron spin of a nitrogen-vacancy centre in diamond to selectively initialize, control and read out carbon-13 spins in the surrounding spin bath and construct high-fidelity single- and two-qubit gates [2]. We exploit these new capabilities to implement a three-qubit quantum-error-correction protocol and demonstrate the robustness of the encoded state against applied errors. These results transform weakly coupled nuclear spins from a source of decoherence into a reliable resource, paving the way towards extended quantum networks and surface-code quantum computing based on multi-qubit nodes. \\[4pt] [1] T. H. Taminiau et al., Phys. Rev. Lett. 109, 137602 (2012)\\[0pt] [2] T. H. Taminiau et al., arXiv:1309.5452 (2013) [Preview Abstract] |
Monday, March 3, 2014 8:36AM - 9:12AM |
A36.00004: Cavity-stimulated Raman emission from a single quantum dot spin Invited Speaker: Timothy Sweeney The integration of solid state quantum emitters into photonic structures represents a scalable path to developing quantum information technologies. Unfortunately, solid state emitters suffer from spectral inhomogeneity, due to spectral wandering of a single emitter or intrinsic dissimilarity between different emitters. In this talk I will present a means to overcome spectral inhomogeneity with a $\Lambda $-type solid-state emitter that is coupled to an optical cavity. For this demonstration we used a charge controlled InAs/GaAs quantum dot that is coupled to a photonic crystal cavity [1]. We exploit a cavity-stimulated Raman process in this $\Lambda $-type system, which allows for the emission of a quantum dot to be detuned from its optical transition by at least 125 GHz [2]. This process not only overcomes spectral inhomogeneity but also can enable an efficient, tunable source of indistinguishable photons and deterministic entanglement of distant spin qubits in a photonic crystal quantum network. \\[4pt] [1] S. G. Carter, et. al., \textit{Quantum control of a spin qubit coupled to a photonic crystal cavity}, Nat. Photonics, vol. 7, no. 4, pp. 329--334, Mar. 2013. \\[4pt] [2] T. M. Sweeney, et. al., \textit{Cavity-stimulated Raman emission from a single quantum dot spin}, (submitted Nov. 2013). [Preview Abstract] |
Monday, March 3, 2014 9:12AM - 9:24AM |
A36.00005: High-selectivity detection of single nuclear spins using rotary echo on a nitrogen-vacancy center in diamond Vagharsh Mkhitaryan, Viatcheslav Dobrovitski The properties of the nitrogen-vacancy (NV) centers in diamond make them an excellent tool for nanoscale spin detection and sensing, capable of detecting individual nuclear spins located 0.5-1 nm away [1]. However, the selectivity of the current methods is limited. We show that the rotating-frame control of the NV center's electron spin can improve the sensing selectivity 10-1000 times in comparison with the existing methods. We employ periodically changing Rabi driving (multiple rotary echo [2]) with a precisely chosen period, corresponding to the precession of the given nuclear spin. The rotary echo decouples the NV center from most nuclear spins, efficiently protecting coherence. At the same time, the given nuclear spin, whose precession fits a stringent resonance condition, does not decouple, and can be detected by its decohering impact on the NV spin. We evaluate the resolution and sensitivity of this detection scheme analytically, and verify the results by numerical simulations. \\[4pt] [1] T. H. Taminiau et al., Phys. Rev. Lett. 109, 137602 (2012), S. Kolkowitz et al., Phys. Rev. Lett. 109, 137601 (2012), N. Zhao et al., Nat. Nanotechnol. 7, 657 (2012), P. London et al., Phys. Rev. Lett. 111, 067601 (2013). \\[0pt] [2] I. Solomon, Phys. Rev. Lett. 2, 301 (1959). [Preview Abstract] |
Monday, March 3, 2014 9:24AM - 9:36AM |
A36.00006: Measurement of the Berry Phase in a Single Solid-State Spin Qubit Kai Zhang, N.M. Nusran, B.R. Slezak, M.V. Gurudev Dutt Geometric phases in quantum mechanics have a long history and may offer some advantages in quantum information processing techniques, e.g. geometric phases are intrinsically robust to fluctuations in control parameters. We demonstrate a controlled way of accumulating geometric phase by Berry's method in a single Nitrogen-Vacancy (NV) center in diamond lattice. We perform state tomography measurement to confirm this Berry phase and we find no evidence for geometric dephasing in our system. [Preview Abstract] |
Monday, March 3, 2014 9:36AM - 9:48AM |
A36.00007: Dual-Channel Lock-in Magnetometry with a Single Spin in Diamond N.M. Nusran, M.V. Gurudev Dutt Diamond spin probes are promising candidates for nanoscale magnetometry and magnetic imaging. Although dynamic decoupling (DD) technique with the spin can lead to high sensitivity ($\sim nT / \sqrt{Hz}$) , certain limitations exist in the standard sensing approach for AC magnetic fields: i) a trade-off between the sensitivity and the dynamic range and ii) constraints on the AC magnetic field phase. We present an experimental scheme that incorporates DD and phase estimation algorithms to address these problems. We achieve nearly decoherence-limited sensitivity over a wide dynamic range, and we also demonstrate unambiguous reconstruction of the amplitude and phase of the magnetic field. [Preview Abstract] |
Monday, March 3, 2014 9:48AM - 10:00AM |
A36.00008: All-optical spin manipulation methods for a solid-state defect spin C.G. Yale, F.J. Heremans, D.J. Christle, D.D. Awschalom, L.C. Bassett, B.B. Buckley, G. Burkard The nitrogen-vacancy (NV) center in diamond is an optically-addressable defect spin with promising applications in quantum information processing and metrology. Here we discuss all-optical methods of dynamically manipulating the spin state of the NV center by exploiting coherent interactions with light at temperatures below 10 K. We study the spin dynamics of the NV center using coherent pulses of light, and achieve rotations of the spin state at sub-nanosecond timescales\footnote{L.C. Bassett*, F.J. Heremans*, D.J. Christle, C.G. Yale, G. Burkard, B.B. Buckley, and D.D. Awschalom, \emph{in preparation} }. With ultrafast pump-probe spectroscopy and by tuning the excited-state spin Hamiltonian with a magnetic field, we demonstrate arbitrary-axis spin rotations and controlled unitary evolution within the full spin-triplet manifold. These experiments also complement recent work demonstrating optical spin control using coherent dark states\footnote{C.G. Yale*, B.B. Buckley*, D.J. Christle, G. Burkard, F.J. Heremans, L.C. Bassett, and D.D. Awschalom, \emph{PNAS} \textbf{110}, 7595 (2013).}. These all-optical techniques provide a probe for decoherence and a pathway toward integrating spin qubits and photonic networks. [Preview Abstract] |
Monday, March 3, 2014 10:00AM - 10:12AM |
A36.00009: Optical studies of ultrafast orbital dynamics of a single spin in diamond F.J. Heremans, D.J. Christle, C.G. Yale, D.D. Awschalom, L.C. Bassett, B.B. Buckley, G. Burkard The nitrogen-vacancy (NV) center in diamond shows great potential as an optically addressable solid-state spin for use in quantum information and metrology. At low temperature ($T < 10$ K) the NV center's orbital-doublet, spin-triplet excited state becomes stable and optically coherent with the ground state. Here we use ultrafast optical pump-probe techniques coupled with optical polarization selection rules to investigate coherent orbital dynamics of the NV center's excited state\footnote{L. C. Bassett*, F. J. Heremans*, D. J. Christle, C. G. Yale, G. Burkard, B. B. Buckley, and D. D. Awschalom, \textit{in preparation}.}. The experiments reveal dynamics which occur on nanosecond down to femtosecond timescales due to the interplay amongst these three orbital levels. These techniques enable all-optical control of the NV center's spin state and could provide a probe to investigate orbital decoherence and phonon interactions in the NV center and other defect systems. [Preview Abstract] |
Monday, March 3, 2014 10:12AM - 10:24AM |
A36.00010: Toward Deterministic Implantation of Nitrogen Vacancy Centers in Bulk Diamond Crystals T.O. Brundage, Z. Atkins, S. Sangtawesin, J.R. Petta Over the last decade, research investigating the room temperature stability, coherence, and optical manipulation of spin states of the nitrogen vacancy (NV) center in diamond has made it a strong candidate for applications in magnetometry and quantum information processing. As research progresses and we begin to investigate the dynamics and scalability of multiple NV systems, the ability to place NV centers deterministically in the host material with high accuracy is critical. Here we implement a simple fabrication method for NV implantation. We expose and develop small dots in PMMA using an electron-beam lithography tool. Unexposed PMMA serves as a mask for 20 keV nitrogen-15 implantation. The implanted sample is then cleaned in a boiling mixture of nitric, sulfuric, and perchloric acid. Annealing at 850$^\circ$ for 2 hours allows vacancies to diffuse next to implanted nitrogen atoms, forming NV centers with an efficiency of a few percent. SRIM simulations provide nitrogen ion distribution within our diamond substrate and PMMA mask as functions of implantation energy. Thus, after balancing implantation parameters and exposure hole cross-sections, NV center placement can be achieved with accuracy limited by the precision of available electron-beam lithography equipment. [Preview Abstract] |
Monday, March 3, 2014 10:24AM - 10:36AM |
A36.00011: Room Temperature Optically-Detected Magnetic Resonance of Silicon Vacancies in SiC Samuel G. Carter, Evan R. Glaser, Brad D. Weaver Single vacancies and vacancy pairs in silicon carbide (SiC) have shown strong potential as quantum bits (qubits) due to demonstrations of spin coherence at room temperature and the maturity of semiconductor device processing in this material system. The majority of work so far on the Si vacancy has still been at low temperatures and high magnetic fields with electron paramagnetic resonance detection, which are not well-suited for many applications. Here, we demonstrate room temperature optically detected magnetic resonance (ODMR) of the Si vacancy in SiC for a series of relatively low magnetic fields. At these fields, there are changes in the ODMR signal due to various effects including the crossing of different spin states. We measure the excitation wavelength dependence and time-dependence of the optical process that orients and detects the spin state, perform microwave pulse control of the spins showing Rabi oscillations, and measure the emission lifetime of the defect to be 6 ns. These results provide a better understanding of the properties of this system and the conditions under which the spin states of the vacancy can be controlled. [Preview Abstract] |
Monday, March 3, 2014 10:36AM - 10:48AM |
A36.00012: Photonic engineering of defect qubit systems in silicon carbide G. Calusine, A. Politi, D.D. Awschalom The recent discovery of electronic states in silicon carbide (SiC) exhibiting properties similar to the negatively charged nitrogen vacancy center in diamond has opened up the possibility of scalable integration of defect qubits into solid state devices that can be fabricated on the wafer scale [1,2]. One form of SiC termed ``3C'' grows as a high quality thin film on silicon making it a promising platform for incorporating these defect systems into three dimensional device architectures such as photonics and micro- and nano-mechanical devices. We present the results of our recent progress towards incorporating optically active defects states in 3C SiC into high Q, small mode volume planar photonic crystal optical cavities. We demonstrate an optimized process for producing modified H1 and L3 cavities with Q's as high as 2700. Additionally, we utilize a combination of resonant scattering spectroscopy techniques and FDTD simulations to study the coupling of defect optical transitions to cavity modes and intrinsic cavity properties. \\[4pt] [1] W. F. Koehl et al., Nature 479, 84-87 (2011)\\[0pt] [2] A. L. Falk et al., Nat. Commun. 4, 1819 (2013) [Preview Abstract] |
Monday, March 3, 2014 10:48AM - 11:00AM |
A36.00013: Electrically driven spin resonance in silicon carbide color centers Paul Klimov, Abram Falk, Bob Buckley, David Awschalom We demonstrate that the spin of optically addressable point defects can be coherently controlled with AC electric fields [1]. Based on magnetic-dipole forbidden spin transitions, this scheme enables spatially confined spin control, the imaging of GHz-frequency resonant electric fields, and the characterization of defect spin multiplicity. Our results are based on the QL1 defect in 6H-SiC, which is one of many newly appreciated paramagnetic defects in SiC that can be optically addressed and exhibit long spin coherence times. Our methods apply generally to optically addressable spin systems in many semiconductors, including the nitrogen-vacancy center in diamond. Since electric fields are readily confined on nanometer scales, electrically driven spin resonance offers a viable route towards scalable quantum control of electron spins in a dense network.\\[4pt] [1] P. V. Klimov et al., arXiv:1310.4844 (2013). [Preview Abstract] |
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