Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A26: Focus Session: Semiconductor Qubits - Optical Hybridization |
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Sponsoring Units: GQI Chair: Thaddeus Ladd, HRL Laboratories, LLC Room: 328 |
Monday, March 18, 2013 8:00AM - 8:36AM |
A26.00001: Observation of quantum dot spin-photon entanglement Invited Speaker: Atac Imamoglu Entanglement plays a central role in the burgeoning field of quantum information processing. A possible route towards a scalable architecture is provided by the concept of distributed quantum computation, based on small-scale few-qubit quantum processor nodes interconnected by single photon pulses. Generation of quantum correlated spin-photon pairs is a key step in such an approach. In this talk, we report the observation of quantum entanglement between a semiconductor quantum dot spin and the color of a propagating optical photon. The demonstration of entanglement relies on the use of fast single-photon detection which allows us to project the photon into a superposition of its two frequency components. Our results extend the previous demonstrations of single-spin photon entanglement in trapped ions, neutral atoms and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nano-structures that allow for on-chip integration of electronic and photonic elements. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 8:48AM |
A26.00002: Entanglement between a single quantum spin and a photon through ultrafast frequency downconversion to telecom wavelengths Kristiaan De Greve, Leo Yu, Peter McMahon, Jason Pelc, Chandra Natarajan, Na Young Kim, Eisuke Abe, Sebastian Maier, Christian Schneider, Martin Kamp, Sven Hoefling, Robert Hadfield, Alfred Forchel, Martin Fejer, Yoshihisa Yamamoto We demonstrate high-fidelity entanglement between a single InAs quantum dot electron spin, and the polarization of a spontaneously emitted single photon. With a magnetic field in Voigt geometry, the quantum dot's excited (trion) states are connected to the spin states in a lambda-configuration. We use these lambda-systems for all-optical spin manipulation, and spontaneous emission from one of the trion states gives rise to entanglement between both the polarization and color of the photon, as well as the spin state. Leakage of which-path information through e.g. the color of the photon obscures the spin-photon-polarization entanglement, which we overcome by a quantum erasure procedure. By time-resolved frequency conversion to a low-fiber-loss wavelength (1560 nm), we measure the photon arrival time with sub-10 ps resolution. Such ultrafast detection is inherently broadband, and incapable of distinguishing between the respective colors of the decay paths, providing the necessary quantum erasure. The conversion to 1560 nm also provides a means to extend the distance over which spin-photon entanglement can be maintained. [Preview Abstract] |
Monday, March 18, 2013 8:48AM - 9:00AM |
A26.00003: Tomography of a high-fidelity spin-photon entangled state Peter McMahon, Kristiaan De Greve, Leo Yu, Jason Pelc, Chandra Natarajan, Na Young Kim, Eisuke Abe, Sebastian Maier, Christian Schneider, Martin Kamp, Sven Hoefling, Robert Hadfield, Alfred Forchel, M.M. Fejer, Yoshihisa Yamamoto The generation of entanglement between a quantum memory and a flying qubit is an important step towards building a quantum repeater node. Entanglement between a photon and a matter qubit has been demonstrated in several systems, including neutral atoms, trapped ions, NV centers and quantum dots. Quantum dots have a natural advantage that their radiative lifetimes are short, and therefore the rate of entanglement generation can be much faster than in other systems. We have recently demonstrated entanglement between an electron spin in a quantum dot, and the polarization of an emitted photon. In addition, the photon is converted to the low-loss 1550 nm band, which is important for implementing long-distance quantum communication systems. In this talk, I will present the reconstruction of the full density matrix of the entangled spin-photon state that we produce. We calculate the fidelity of the state from the density matrix, and conclude that it is $>90\%$. [Preview Abstract] |
Monday, March 18, 2013 9:00AM - 9:12AM |
A26.00004: Ultrafast downconversion quantum interface for a single quantum dot spin and 1550-nm single-photon channel L. Yu, J.S. Pelc, K. De Greve, P.L. McMahon, M.M. Fejer, Y. Yamamoto, S. Maier, C. Schneider, M. Kamp, S. Hofling, A. Forchel, C.M. Natarajan, R.H. Hadfield Long-distance quantum communication networks require appropriate interfaces between matter qubit-based nodes and low-loss photonic quantum channels. Quantum frequency conversion (QFC), whereby a photonic qubit's carrier frequency is translated while maintaining its quantum state, is well-suited to the task. Quantum dots have been studied extensively as potential quantum network nodes, but they do not emit indistinguishable single photons at telecomm wavelengths. We report an ultrafast, low-noise downconversion quantum interface, in which 910-nm single photons from a quantum dot are downconverted to the 1.5-$\mu$m lowest-loss telecom band, showing near-perfect preservation of antibunched photon statistics. Moreover, the resulting time resolution could also improve photon indistinguishability. Together with the III-V semiconductor quantum dot spin system, this ultrafast downconversion quantum interface provides new possibility to realize long-distance quantum communication networks. [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:24AM |
A26.00005: Observation of quantum entanglement between a photon and a single electron spin confined to an InAs quantum dot John Schaibley, Alex Burgers, Greg McCracken, Luming Duan, Paul Berman, Duncan Steel, Allan Bracker, Daniel Gammon, Lu Sham A single electron spin confined to a single InAs quantum dot (QD) can serve as a qubit for quantum information processing. By utilizing the QD's optically excited trion states in the presence of an externally applied magnetic field, the QD spin can be rapidly initialized, manipulated and read out. A key resource for quantum information is the ability to entangle distinct QD spins. One approach relies on intermediate spin-photon entanglement to mediate the entanglement between distant QD spin qubits. We report a demonstration of quantum entanglement between a photon's polarization state and the spin state of a single electron confined to a single QD. Here, the photon is spontaneously emitted from one of the QD's trion states. The emitted photon's polarization along the detection axis is entangled with the resulting spin state of the QD. By performing projective measurements on the photon's polarization state and correlating these measurements with the state of the QD spin in two different bases, we obtain a lower bound on the entanglement fidelity of 0.59 (after background correction). The fidelity bound is limited almost entirely by the timing resolution of our single photon detector. The spin-photon entanglement generation rate is $3 \times 10^{3}$ s$^{-1}$. [Preview Abstract] |
Monday, March 18, 2013 9:24AM - 9:36AM |
A26.00006: A Spin Qubit Coupled to a Photonic Crystal Cavity Timothy Sweeney, Samuel Carter, Mijin Kim, Chul Soo Kim, Dmitry Solenov, Sophia Economou, Thomas Reineke, Lily Yang, Allan Bracker, Daniel Gammon The development of a scalable light-matter quantum interface is an important goal of quantum information research. Photonic crystal (PC) membranes provide an architecture in which the interaction of photons with an optically active matter qubit can be controlled through the introduction of optical cavities and waveguides. Charge neutral quantum dots are commonly integrated into PC architectures and are useful for sources and switches, but do not demonstrate long-lived coherences. A charged quantum dot in a PC environment could lead to a spin-photon quantum interface, where it is the long-lived spin of the electron, not the exciton that serves as a qubit. We demonstrate optical spin initialization and coherent control of an electron in a quantum dot that is embedded in and coupled to a 2D PC membrane cavity. The PC membrane is incorporated into an asymmetric NIP diode that allows for charging of an InAs quantum dot via an applied bias. Resonant laser spectroscopy performed in a transverse magnetic field enables the optical measurement and initialization of the electron spin. Furthermore, with the introduction of detuned control pulses, we perform coherent rotations of the electron spin state. These studies demonstrate several essential accomplishments toward a spin-photon interface. [Preview Abstract] |
Monday, March 18, 2013 9:36AM - 9:48AM |
A26.00007: Quantum Dots in H1 Photonic Crystal Microcavities for Quantum Information Jenna Hagemeier, Cristian Bonato, Tuan-Anh Truong, Hyochul Kim, Morten Bakker, Gareth J. Beirne, Martin P. van Exter, Pierre Petroff, Dirk Bouwmeester Coupling semiconductor quantum dots to optical microcavities is a promising technique for implementing quantum information processing protocols in the solid-state. By placing one or more emitters in a cavity, it is possible to create an efficient source of single photons or to explore collective interactions of few-emitter systems. Our devices consist of two layers of quantum dots, embedded in the cavity region of H1 photonic crystal microcavities. One of the quantum dot layers can be frequency-tuned deterministically, allowing two resonant quantum dots to be coupled to a single cavity mode. Because good mode-matching between the cavity mode and the input/output channel is necessary for many applications, we optimize the far-field profiles of our H1 cavities and demonstrate strong enhancement of the external mode matching properties. We will discuss our far-field optimization results as well as our ongoing work to study interactions of multiple emitters in a cavity. [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:00AM |
A26.00008: Dynamical effects of Stark-shifted quantum dots strongly coupled to photonic crystal cavities Kaushik Roy Choudhury, Ranojoy Bose, Edo Waks Single semiconductor quantum-dots (QDs) strongly coupled to photonic crystal cavities are a strong candidate for single photon generation, ultra-fast all optical switching and quantum information processing. Recent experiments on coupled-cavity quantum dot systems show possible manipulation of emission wavelength of the dot through optical Stark effect. Interesting dynamical features arise when the Stark pulse duration is comparable to QD-cavity interaction time. Here, we present a theoretical treatment of these dynamical effects and investigate dynamical emission spectrum, energy transfer and single photon generation. We study these effects through numerical solution of the full master equation. We demonstrate that dynamic Stark effects can be used to generate ultra-fast indistinguishable single photons using rapid Stark tuning of the quantum dot. The theoretical limit for the speed is shown to be faster than adiabatic rapid passage technique used for microwave photon generation in circuit QED. A systematic study of role of device parameters such as pulse-shape, dot-cavity coupling and incoherent losses on the efficiency and speed of single photon generation is also presented for possible experimental realization. [Preview Abstract] |
Monday, March 18, 2013 10:00AM - 10:12AM |
A26.00009: Optical tuning of single quantum dots coupled to photonic crystal molecules using the optical Stark effect Ranojoy Bose, Kaushik Roy, Tao Cai, Glenn S. Solomon, Edo Waks The interaction of semiconductor quantum dots (QD) with photonic crystal resonator systems provides a highly integrated, solid-state platform for studies in ultra-low energy nonlinear optics and quantum optical phenomena. Here, we present a method to tune a semiconductor quantum dot (QD) all-optically into resonance with a cavity mode using the non-resonant optical Stark effect. We use a system comprised of two evanescently coupled photonic crystal cavities containing a single QD in one of the cavities. One mode of the coupled cavity system is used to generate a cavity-enhanced optical Stark shift, enabling the QD to be resonantly tuned to the other cavity mode. We show that the optical tuning of the QD results in a large radiative enhancement of the QD photon emission via the Purcell effect. We will further discuss dynamic experiments in the system using a Stark laser that has a time-duration on the order of the system decay rates. We will show that under this scenario, the cavity-QD spectrum provides a rich array of information on the system dynamics. The experiments are promising for a variety of applications in highly-efficient single photon generation, cavity quantum electrodynamics, ultra-fast optical switching, and classical and quantum information processing. [Preview Abstract] |
Monday, March 18, 2013 10:12AM - 10:24AM |
A26.00010: Controlling interactions between coupled photonic crystal cavities using photochromic tuning Tao Cai, Ranojoy Bose, Glenn Solomon, Edo Waks Strongly coupled photonic crystal (PhC) resonator systems provide a promising platform for studying cavity quantum electrodynamics (QED) using semiconductor quantum dots (QDs). These device structures enable important applications such as photon blockade, quantum simulation, quantum-optical Josephson interferometer, and quantum phase transition of light. Many of these applications require the ability to accurately tune the resonant frequencies of individual cavities in the array, which provides a method to control their coupling interactions. This tuning method must be sufficiently local to address individual cavities spaced by less than 1 micron spatial separation. Here, we present a method for controlling the coupling interaction of photonic crystal cavity arrays by using a local and reversible photochromic tuning technique. By locally altering the refractive index of the photochromic material all-optically, the coupling interaction between two cavity modes could be modified over a tuning range as large as 700 GHz. By using this technique, we demonstrate the ability to couple photonic crystal cavities with a normal mode splitting of only 31.50 GHz. We further demonstrate that this tuning method can be extended to control the coupling interaction in larger cavity arrays. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 10:36AM |
A26.00011: A qubit-photon controlled-NOT gate using a quantum dot strongly coupled to a cavity Hyochul Kim, Ranojoy Bose, Thomas Shen, Glenn Solomon, Edo Waks Strong interactions between matter quantum bits (qubits) and photons play an essential role in quantum information. Quantum dots (QDs) provide a promising implementation of a matter qubit that can be strongly coupled to optical nanocavities, providing a direct light-matter interface. We use this light-matter interface to demonstrate a picosecond timescale controlled NOT logic gate between a QD and a photon, which is a fundamental building block for complex quantum logic. Coherent control of the QD qubit state by optical pulses results in a modification of cavity reflectivity, enabling a conditional bit-flip on the polarization state of a photon incident on the cavity. [Preview Abstract] |
Monday, March 18, 2013 10:36AM - 10:48AM |
A26.00012: All-optical, arbitrary-basis initialization and readout of a diamond spin qubit C.G. Yale, B.B. Buckley, D.J. Christle, F.J. Heremans, L.C. Bassett, D.D. Awschalom, G. Burkard The nitrogen-vacancy (NV) center in diamond is a promising spin qubit candidate, in large part due to its optical addressability via a spin-selective intersystem crossing. Here we demonstrate a general all-optical technique to initialize and readout the NV spin state along an arbitrarily-chosen basis using coherent light fields\footnote{C. G. Yale*, B. B. Buckley*, D. J. Christle, G. Burkard, F. J. Heremans, L. C. Bassett, and D. D. Awschalom (submitted)} below 10 K, which negates the need for this special addressability. By tuning the NV center's excited-state structure to a lambda ($\Lambda$) configuration with a magnetic field, we use coherent population trapping (CPT) to initialize its spin into any desired superposition. We investigate the CPT time dynamics and use quantum state tomography to characterize the resultant state. We also demonstrate spin-state readout along an arbitrarily-chosen basis by measuring photoluminescence emitted during the transient period of the CPT interaction. Since these techniques do not rely on the intersystem crossing, they provide a pathway for all-optical control of other potential defect spin qubits, which may lack the NV center's unique structure. [Preview Abstract] |
Monday, March 18, 2013 10:48AM - 11:00AM |
A26.00013: Defect qubit-nanophotonic structures based on silicon carbide G. Calusine, A. Politi, D.D. Awschalom Defect qubits in silicon carbide (SiC) have recently emerged as a promising alternative to the nitrogen vacancy center in diamond for applications in solid state quantum information technologies\footnote{W. F. Koehl, B.B Buckley, F.J Heremans, G. Calusine, and D.D. Awschalom, \textit{Nature} \textbf{479}, 84-87 (2011)}. One common polytype of SiC, commonly referred to as 3C, is commercially available as a high quality single crystal epitaxial film grown on silicon substrates. We demonstrate that various techniques used to create, polarize, manipulate, and measure nitrogen vacancy centers can be similarly applied to defect spin qubits in 3C silicon carbide, even up to room temperature\footnote{A. L. Falk, B.B. Buckley, G. Calusine, W.F. Koehl, V.V. Dobrovitski, A. Politi, and D.D. Awschalom, (submitted)}. Additionally, we exploit 3C SiC's availability as a heteroepitaxial layer on silicon to incorporate these defect qubits into nanophotonic devices. We present the results of simulations and measurements on nano-fabricated optical devices incorporating defect qubits. These results demonstrate a promising route towards silicon carbide based hybrid light-matter quantum systems. [Preview Abstract] |
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