Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X17: Semiconducting Qubits II |
Hide Abstracts |
Sponsoring Units: GQI Chair: Xuedong Hu, University of Buffalo Room: 318 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X17.00001: Effect of Substrate Doping in Relaxed SiGe Buffers on Strained Si 2DEG Quantum Devices Kun Yao, Mikhail Gaevski, Alexander Chernyshov, Leonid Rokhinson, Curtin Mike, Ji-Soo Park, James Fiorenza, Anthony Lochtefeld, James Sturm We describe the impact of Si substrate doping on the substrate leakage in strained Si two-dimensional electron gases (2DEG) on SiGe relaxed graded buffers and on quantum devices fabricated from the 2DEG. The best commercially available high quality SiGe relaxed buffers with 30{\%} Ge content, grown at temperature above 1000$^{o}$C, have very low threading dislocation density ($<$1E5cm$^{-2})$. Subsequent strained Si/SiGe heterostructures were grown at 625-700$^{o}$C in a rapid thermal chemical vapor deposition (RTCVD). However, it is shown that the substrate doping (Arsenic) contributes to leakage current origin in relaxed buffers at liquid helium temperatures if the starting Si substrate is heavily doped ($\sim $5E17cm$^{-2})$. The leakage can be attributed to enhanced dopant diffusion along misfit dislocations and high diffusion rate of As in SiGe. The leakage current makes side gating of nanostructures in the 2DEG impossible. With a lightly doped substrate, to avoid leakage, we achieved a high quality 2DEG and successful side gating of a 2DEG quantum dot for a quantum point contact. This work is supported by the NSA under ARO contract number W911NF-05-1-0437. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X17.00002: Robust Fabrication Techniques for Si/SiGe Quantum Dots Mingyun Yuan, Feng Pan, Tim Gilheart, Joel Stettenheim, Mustafa Bal, D. E. Savage, M. A. Eriksson, A. J. Rimberg Si/SiGe quantum dots promise a long spin coherence time due to reduced electron-nuclear spin interaction. Nevertheless, successful device yield has been limited in this novel material system due to difficulties in producing reliable ohmic contacts and Schottky gates. We have successfully developed fabrication processes that produce robust ohmic contacts and non-leaky Schottky gates. The ohmic contacts typically have a two-probe resistance of a few tens of kiloohms and the Schottky gates have no detectable leakage current up to an applied voltage of -5 V. In typical devices we are able to pinch off the quantum point contacts with a voltage range between -1.5 V to -4.5 V. Recent experimental results will be discussed. This work was supported by the NSF under Grant No. DMR-0804488, by the NSA, LPS and ARO under Agreement No. W911NF-04-1-0389, and by the ARO under Agreements No. W911NF-06-1-0312 and No. W911NF-06-01-0361. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X17.00003: Effect of Intervalley Mixing on Qubit Operation in SiGe Quantum Dot Structures A. A. Kiselev, R. S. Ross, B. H. Fong, M. F. Gyure We analyze the effects of valley degeneracy and intervalley mixing on single- and multi-electron states in (001) SiGe heterostructures, including effect of interface steps and variations in interface quality. We focus on the structure of two-electron states in both single and double quantum dot structures in the presence of valley degeneracy in the host material and the oscillatory behavior of exchange coupling in the presence of nonplanar heterointerfaces. We present modeling and simulation results relevant to the design of SiGe based accumulation-mode quantum-dot structures, especially CI calculation in presence of the intervalley mixing. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X17.00004: Transport and charge sensing in Si/SiGe double-quantum dots Christie Simmons, Madhu Thalakulam, E. K. Sackmann, B. J. Van Bael, D. E. Savage, M. G. Lagally, R. Joynt, M. Friesen, S. N. Coppersmith, M. A. Eriksson Gated quantum dots in Si/SiGe are of interest because spins in silicon are weakly coupled to the host material. We demonstrate that Coulomb blockade measurements through a single quantum dot are well correlated with charge sensing in a nearby quantum point contact. Charge sensing enables the determination of the absolute number of electrons in the system, and we present data demonstrating a one-electron single quantum dot. Incorporated with a double quantum dot, charge sensing can be used to probe the inter-dot motion of a single electron at fixed total charge in the double dot. The tunnel coupling between the two dots directly effects the charge localization and thus the sharpness of this inter-dot transition. Here we demonstrate gated electrical control of the exchange coupling -- an important step towards qubit implementation -- showing a smooth transition between two well-isolated dots, two dots so strongly coupled that they act as a single large quantum dot, and the intermediate regime. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X17.00005: Transient and stationary leakage current through a double quantum dot in the Pauli spin blockade regime Farzad Qassemi Maloomeh, William A. Coish, Frank K. Wilhelm We have calculated stationary and transient leakage current through a double quantum dot in the Pauli spin blockade regime. Quite remarkably, even in systems with inhomogeneous hyperfine coupling, we find that the leakage current is often controlled by spin-flip cotunneling processes with the leads. Our calculations show that these processes can be suppressed for one of the spin-triplet states by applying a small magnetic field, allowing for the preparation of a pure spin triplet. We have also found the transient effective charge passing through the double dot between blocking events, which can be strongly modified due to the spin-flip cotunneling processes. These results may explain features observed in several experiments. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X17.00006: ABSTRACT WITHDRAWN |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X17.00007: Energy Dependent Tunneling in a Silicon Double Quantum Dot Mark Friesen, C. B. Simmons, Nakul Shaji, R. H. Blick, S. N. Coppersmith, M. A. Eriksson We study transport currents in a few-electron Si/SiGe double quantum dot. A detailed analysis is made of the recently discovered phenomenon of lifetime enhanced transport (LET), in which current may flow in a regime typically considered to be blockaded. To understand this effect, a rate equation model is developed, including both singlet and triplet transport channels. Making use of a simple model of tunneling across a quantum barrier, we map out the energy dependence of the tunneling. This allows us to obtain quantitative estimates for the tunneling rates and transport currents throughout the reverse bias regime. We are then able to identify both resonant and non-resonant phenomena, and provide a physical understanding of the different blockade regimes. In particular, we provide detailed predictions for the conditions under which LET may be observed. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X17.00008: Charge transport in silicon double quantum dots Ted Thorbeck, Neil Zimmerman, Akira Fujiwara, Yukinori Ono, Yasuo Takahashi, Hiroshi Inokawa Double quantum dots are an essential component for many schemes of semiconductor quantum computation. We will present results for transport through a silicon double quantum dot system. Our devices are formed by mesa-etching an SOI wafer to form a nanowire, and then poly-silicon gates are deposited. A global gate is used to invert and local gates form tunnel barriers isolating quantum dots and controlling the potential of the dots. Because the coupling between the two dots is controllable, a transition from a single dot, to two coupled dots, to two uncoupled dots is observed. We will analyze the resulting honeycomb diagram. We also hope to present results in the few electron regime. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X17.00009: Modeling of Accumulation-Mode Quantum Dot Structures for Quantum Information Processing R.S. Ross, A.A. Kiselev, B.H. Fong, M.F. Gyure We present modeling and simulation results relevant to the design of SiGe and III-V based accumulation-mode quantum-dot structures for use as electron-spin-based qubits. We have developed a self-consistent real-space multi-electron simulation tool to efficiently explore and optimize these structures. Specific practical issues we address include the design of double-quantum-well heterostructures, enhancement-gate-electrode design and quantum-dot electronic structure with attention to the effects of electrostatic gate action. We examine the addition and excited-state spectra of single quantum dots (QD), the exchange coupling of nearest-neighbor quantum dots and the vertical tunneling behavior of our accumulation-mode devices. We also present comparisons to recently obtained experimental results on addition spectra in accumulation-mode quantum dots and show that our models correctly capture the relevant behavior. In addition, we address the robustness of device designs with respect to randomly distributed discrete dopants using a semi-analytical model and full numerical simulation based on impurity-induced random potentials. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X17.00010: Si double quantum dot spin qubit in a MOSFET structure Qiuzi Li, Dimitirie Culcer, Lukasz Cywinski, Sankar Das Sarma Motivated by recent experimental developments, we theoretically consider the prospects for creating spin qubits in a lateral double-dot structure fabricated in a Si MOSFET by lithographic patterning. We calculate tunnel coupling, exchange splitting, and other relevant qubit properties as functions of the double-dot structural parameters, i.e. dot separation, central barrier, detuning, etc. Our motivation is to obtain a detailed qualitative comparison between GaAs and Si double-dot systems to see whether a Si MOSFET double-dot structure is feasible as a spin qubit in real quantum computer architectures. We will discuss both regular single electron spin qubit and the successful (in GaAs quantum dots) singlet-triplet spin qubits. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X17.00011: Accumulation-Mode Quantum-Dot Devices Matthew Borselli, Edward Croke, Mark Gyure, Robert Hayes, Ivan Milosavljevic, Adele Schmitz, Jeong-Sun Moon, Andrew Hunter We have developed a quantum-dot device based on a double-well heterostructure in which electrons are localized in the top, mostly empty well by forward biasing a small circular gate. Charge occupancy changes in the dot are monitored by measuring current confined to a narrow channel in the bottom well. In this design, dot occupancy is primarily controlled by a single gate and interacting dots can be straightforwardly fabricated. We have successfully fabricated and characterized single-dot devices of this design in AlGaAs/InGaAs, and are extending the design to SiGe/Si heterostructures. We have measured charging spectra of III-V versions of the device down to zero electron occupancy. Charging spectra show enhanced stability for n=2, 6, 12, and 20 electrons. We have measured the tunneling times as a function of bias to map out excited states of a two-electron dot. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X17.00012: Cross-correlation heterodyne detection part I: Measuring the vacuum fluctuations at microwave frequencies Matteo Mariantoni, Edwin P. Menzel, M. A. Araque Caballero, F. Deppe, E. Hoffmann, T. Niemczyk, A. Marx, R. Gross, E. Solano In order to gain a profound insight into the fundamental properties of quantum electrodynamics (QED), studying the zero-point fluctuations of microwave radiation represents an important task. Here, we present a full experimental characterization of the vacuum fluctuations by measuring the Planck distribution of its noise power at microwave frequencies and very low temperatures. We observe a cross-over from thermal noise to vacuum quantum noise and quantify the level of vacuum fluctuations for a narrow frequency band centered around 5.85 GHz. We demonstrate the change of the vacuum fluctuations level with the center frequency. Finally, we perform a new type of heterodyne detection particularly suitable for circuit QED systems. It is based on microwave beam splitters and cross-correlation measurements and allows for the reconstruction of the entire covariance matrix of the vacuum. We acknowledge support from SFB631, NIM, EuroSQUIP, and the Ikerbasque Foundation. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X17.00013: Cross-correlation heterodyne detection part II: Measuring microwave nontrivial propagating signals Edwin P. Menzel, Matteo Mariantoni, M. A. Araque Caballero, F. Deppe, E. Hoffmann, T. Niemczyk, A. Marx, R. Gross, E. Solano The accurate measurement of the first two moments of Gaussian states (e.g., coherent or squeezed states) allows for their complete characterization. This provides a tool to clarify the quantum nature of microwave radiation, an important issue for example in circuit quantum electrodynamics. We present a full experimental characterization of nontrivial microwave signals with an average photon number of the order of 1, whose variance exhibits an elaborate dependence on external control parameters. We experimentally access the entire covariance matrix by splitting the input signals via microwave beam splitters and performing cross-correlation measurements. In this manner, we are able to precisely resolve the first two moments, a challenging task at microwave frequencies. Furthermore, we succeeded to measure the third central moment of similar nontrivial signals. We acknowledge support from SFB631, NIM, EuroSQUIP, and the Ikerbasque Foundation. [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X17.00014: High precision interferometry with a transition edge sensor Christoph F. Wildfeuer, Aaron J. Pearlman, Jun Chen, Jonathan P. Dowling, Jingyun Fan, Alan Migdall In this contribution, we present our studies of Michelson and Fabry-Perot interferometers with a photon-number resolving detector. We show experimentally that with a weak coherent light beam, the use of a photon-number resolving detector improves the interferometric resolution. We also discuss ways the sensitivity of interferometers can be further improved beyond the standard quantum limit by using nonclassical light and photon-number resolving detectors. ~ [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700