Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session W37: Focus Session: Semiconductor Qubits - Gated Dots and Impurities II |
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Sponsoring Units: GQI Chair: Charles Tahan, Laboratory for Physical Sciences Room: 212A |
Thursday, March 5, 2015 2:30PM - 3:06PM |
W37.00001: Theory of the Quantum Dot Hybrid Qubit Invited Speaker: Mark Friesen The quantum dot hybrid qubit, formed from three electrons in two quantum dots, combines the desirable features of charge qubits (fast manipulation) and spin qubits (long coherence times). The hybridized spin and charge states yield a unique energy spectrum with several useful properties, including two different operating regimes that are relatively immune to charge noise due to the presence of optimal working points or ``sweet spots.'' In this talk, I will describe dc and ac-driven gate operations of the quantum dot hybrid qubit. I will analyze improvements in the dephasing that are enabled by the sweet spots, and I will discuss the outlook for quantum hybrid qubits in terms of scalability. \\[4pt] This work was supported in part by ARO (W911NF-12-0607), NSF (PHY-1104660), the USDOD, and the Intelligence Community Postdoctoral Research Fellowship Program. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies or endorsements, either expressed or implied, of the US government. [Preview Abstract] |
Thursday, March 5, 2015 3:06PM - 3:18PM |
W37.00002: Rabi oscillations at different tunnel couplings for an ac-gated quantum dot qubit Brandur Thorgrimsson, Dohun Kim, C.B. Simmons, Daniel R. Ward, Ryan H. Foote, D.E. Savage, M.G. Lagally, Mark Friesen, S.N. Coppersmith, M.A. Eriksson One way to create a qubit is to use two distinct positions of a single electron as qubit states. Such a system can be achieved by using the left and right positions in a gated double quantum dot. In this system the qubit is strongly coupled to electric fields and has potential for high-speed operations. By tuning specific gate voltages, the tunnel coupling between the left and right quantum dots can be changed. Here, by using resonant ac microwave driving and gate tuning, we explore variations of T2* and the Rabi frequency on the tunnel coupling and microwave drive power, and we study strong driving effects such as generation of second harmonics. This work was supported in part by ARO (W911NF-12-0607) and NSF (DMR-1206915 and PHY-1104660). Development and maintenance of the growth facilities used for fabricating samples is sup- ported by DOE (DE-FG02-03ER46028). This research utilized NSF-supported shared facilities at the University of Wisconsin-Madison. [Preview Abstract] |
Thursday, March 5, 2015 3:18PM - 3:30PM |
W37.00003: Single-electron spin resonance in a Si/SiGe double quantum dot with a micromagnet Kenta Takeda, Jun Kamioka, Toshiaki Obata, Tomohiro Otsuka, Takashi Nakajima, Matthieu Delbecq, Shinichi Amaha, Jun Yoneda, Akito Noiri, Retsu Sugawara, Tetsuo Kodera, Shunri Oda, Seigo Tarucha Electrons in Si quantum dots are promising candidates for implementing spin qubits because of their long coherence times [1, 2]. We report on our measurement results of addressable electron spin resonance in a Si/SiGe double quantum dot with a micromagnet. We also show that the addressable electron spin resonance is useful to understand two-electron spin and valley states in Si double quantum dot. [1] E. Kawakami \emph{et al.}, Nat. Nanotech. (2014), [2] M. Veldhorst \emph{et al.}, Nat. Nanotech. (2014) [Preview Abstract] |
Thursday, March 5, 2015 3:30PM - 3:42PM |
W37.00004: Hybrid Spin and Valley Quantum Computing with Singlet-Triplet Qubits Niklas Rohling, Maximilian Russ, Guido Burkard The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations [1].\\[4pt] [1] N. Rohling, M. Russ, and G. Burkard, Phys. Rev. Lett. \textbf{113}, 176801 (2014) [Preview Abstract] |
Thursday, March 5, 2015 3:42PM - 3:54PM |
W37.00005: Singlet-triplet donor-quantum-dot qubit in silicon Patrick Harvey-Collard, Gregory A. Ten Eyck, Joel R. Wendt, Tammy Pluym, Michael P. Lilly, Malcolm S. Carroll, Michel Pioro-Ladri\`ere Electron spins bound to phosphorus (P) donors in silicon (Si) are promising qubits due to their high fidelities, but donor-donor coupling is challenging. We propose an alternative two-electron singlet-triplet quantum-dot (QD) and donor (D) hybrid qubit. A QD is formed at a MOS 28-Si interface and is tunnel-coupled to implanted P. The proposed two-axis system is defined by the exchange and contact hyperfine interactions. We demonstrate that a few electron QD can be formed and tuned to interact with a donor. We investigate the spin filling of the QD-D system through charge-sensed (CS) magnetospectroscopy and identify spin-up loading consistent with a singlet-triplet splitting of $\sim$100 $\mu$eV near a QD-D anti-crossing. We also demonstrate an enhanced CS readout contrast and time window due to the restricted relaxation path of the D through the QD. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 5, 2015 3:54PM - 4:06PM |
W37.00006: Coupling a Si/SiGe quantum dot to an implanted phosphorus donor Ryan H. Foote, Daniel R. Ward, Brandur Thorgrimsson, J.R. Prance, Andre Saraiva, D.E. Savage, Mark Friesen, S.N. Coppersmith, M.A. Eriksson We have fabricated quantum dots in a Si/SiGe heterostructure both with and without implanted phosphorus donors. We present the results of transport measurements at dilution refrigerator temperatures through both types of devices. In one device we see evidence of coupling between a dot and a localized state consistent with a donor. We present estimates of the position of the localized state using Coulomb blockade measurements as a function of several different gate voltage configurations. This research supported in part by NSF (DMR-1206915) and ARO (W911NF-12-1-0607). Development and maintenance of the growth facilities used for fabricating samples is supported by DOE (DE-FG02-03ER46028). This research utilized facilities supported by the NSF (DMR-1121288). [Preview Abstract] |
Thursday, March 5, 2015 4:06PM - 4:18PM |
W37.00007: Few electron quantum dot coupling to donor implanted electron spins Martin Rudolph, Patrick Harvey-Collard, Erik Neilson, John Gamble, Richard Muller, Toby Jacobson, Greg Ten-Eyck, Joel Wendt, Tammy Pluym, Michael Lilly, Malcolm Carroll Donor-based Si qubits are receiving increased interest because of recent demonstrations of high fidelity electron or nuclear spin qubits and their coupling. Quantum dot (QD) mediated interactions between donors are of interest for future coupling of two donors. We present experiment and modeling of a polysilicon/Si MOS QD, charge-sensed by a neighboring many electron QD, capable of coupling to one or two donor implanted electron spins (D) while tuned to the few electron regime. The unique design employs two neighboring gated wire FETs and self-aligned implants, which supports many configurations of implanted donors. We can access the (0,1)$\Leftrightarrow $(1,0) transition between the D and QD, as well as the resonance condition between the few electron QD and two donors ((0,N,1)$\Leftrightarrow $(0,N$+$1,0)$\Leftrightarrow $(1,N,0)). We characterize capacitances and tunnel rate behavior combined with semi-classical and full configuration interaction simulations to study the energy landscape and kinetics of D-QD transitions. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. The work was supported by the Sandia National Laboratories Directed Research and Development Program. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the U. S. Department of Energy under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 5, 2015 4:18PM - 4:30PM |
W37.00008: Device-Level Models Using Multi-Valley Effective Mass Andrew D. Baczewski, Adam Frees, John King Gamble, Xujiao Gao, N. Tobias Jacobson, John A. Mitchell, In\`{e}s Monta\~{n}o, Richard P. Muller, Erik Nielsen Continued progress in quantum electronics depends critically on the availability of robust device-level modeling tools that capture a wide range of physics and effective mass theory (EMT) is one means of building such models. Recent developments in multi-valley EMT show quantitative agreement with more detailed atomistic tight-binding calculations of phosphorus donors in silicon (Gamble, et. al., arXiv:1408.3159). Leveraging existing PDE solvers, we are developing a framework in which this multi-valley EMT is coupled to an integrated device-level description of several experimentally active qubit technologies. Device-level simulations of quantum operations will be discussed, as well as the extraction of process matrices at this level of theory. The authors gratefully acknowledge support from the Sandia National Laboratories Truman Fellowship Program, which is funded by the Laboratory Directed Research and Development (LDRD) Program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 5, 2015 4:30PM - 4:42PM |
W37.00009: Multi-valley effective mass theory for device-level modeling of open quantum dynamics N. Tobias Jacobson, Andrew D. Baczewski, Adam Frees, John King Gamble, Ines Montano, Jonathan E. Moussa, Richard P. Muller, Erik Nielsen Simple models for semiconductor-based quantum information processors can provide useful qualitative descriptions of device behavior. However, as experimental implementations have matured, more specific guidance from theory has become necessary, particularly in the form of quantitatively reliable yet computationally efficient modeling. Besides modeling static device properties, improved characterization of noisy gate operations requires a more sophisticated description of device dynamics. Making use of recent developments in multi-valley effective mass theory, we discuss device-level simulations of the open system quantum dynamics of a qubit interacting with phonons and other noise sources. [Preview Abstract] |
Thursday, March 5, 2015 4:42PM - 4:54PM |
W37.00010: Multi-valley effective mass treatment of donor-dot tunneling in silicon Adam Frees, Andrew D. Baczewski, John King Gamble, N. Tobias Jacobson, Richard P. Muller, Erik Nielsen Many cutting-edge experiments in silicon-based devices for quantum information processing involve the tunneling of an individual electron from a donor atom within the material to the interface of the heterostructure. Understanding how this tunneling process varies among different realistic devices is therefore of great interest. Using a multi-valley effective mass approximation method, we find the tunnel coupling, adiabatic min-gap, and ionizing electric field strength between a phosphorous donor in silicon and a nearby quantum dot at a Si/SiO$_2$ interface. Additionally, we calculate these quantities for a phosphorous donor in strained silicon and a Si/SiGe interface. We consider how these properties change as a function of relative position between the donor and the dot. The authors gratefully acknowledge support from the Sandia National Laboratories Truman Fellowship Program, which is funded by the Laboratory Directed Research and Development (LDRD) Program. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Thursday, March 5, 2015 4:54PM - 5:06PM |
W37.00011: Electron spin coherence of shallow donors in germanium A.J. Sigillito, R.M. Jock, A.M. Tyryshkin, K.M. Itoh, S.A. Lyon The presence of magnetic nuclei is one major source of electron and nuclear spin decoherence in semiconductors. Germanium is one of the few semiconductor materials that can be isotopically enriched to have no magnetic nuclear isotopes, making it a promising material for quantum computing applications. In this talk we report T$_{1}$ and T$_{2}$ relaxation times for $^{75}$As and $^{31}$P donors in natural Ge and isotopically enriched $^{74}$Ge for temperatures down to 350 mK. We find that T$_{1}$ is limited by a direct phonon process at these temperatures, in agreement with previous reports. Above 2K, the coherence time for donor spins is limited by T$_{1}$, while below 2K it is limited by spectral diffusion from $^{73}$Ge nuclear spins. In isotopically-enriched $^{74}$Ge (3.8{\%} residual $^{73}$Ge) we find a T$_{2}$ of 110 us for $^{75}$As donors. Electron Spin Echo Envelope Modulation (ESEEM) data will be presented identifying the hyperfine coupling of the donor electron to several $^{73}$Ge lattice sites with couplings ranging from 200 kHz to 1 MHz. [Preview Abstract] |
Thursday, March 5, 2015 5:06PM - 5:18PM |
W37.00012: Spin ensembles as sensitive probes of environmental magnetic field noise Abraham Asfaw, Gary Wolfowicz, John J. L. Morton, Alexei Tyryshkin, Stephen Lyon Environmental magnetic field noise makes quantum control of electron and nuclear spins difficult. Conversely, the sensitivity of spins to small magnetic fields implies that they can be used as sensitive probes of magnetic field fluctuations. We report spin resonance measurements of donors in silicon showing that the phase information in single-shot measurements of spin ensembles combined with quadrature detection can yield useful information about environmental noise. By measuring the accumulated phase statistics with time, we extract the power spectrum of the environmental magnetic field noise. The range of noise frequencies probed in this way is set by the magnetic moment of the spins. We measure the noise power spectrum at high frequencies (100 Hz - 10 kHz) using electron spins and at low frequencies (1 - 100 Hz) using nuclear spins. We also show that a broadband measurement of the noise power spectrum can be obtained by tuning the magnetic moment of electron spins in bismuth donors over a wide range from 0.01 to 1 electron magnetic moment. Our method, which uses the full statistics of the accumulated phase, can be viewed as complementary to existing dynamical decoupling schemes which use filter functions to probe the noise power spectrum. [Preview Abstract] |
Thursday, March 5, 2015 5:18PM - 5:30PM |
W37.00013: Mechnical tuning of ionized donors in silicon David P. Franke, Florian M. Hrubesch, Markus Kuenzl, Kohei M. Itoh, Felix Hoehne, Lukas Dreher, Martin S. Brandt Ionized donors in silicon have been shown to have extraordinarily long coherence times, exceeding tens of minutes even at room temperature, which, combined with the very advanced state of silicon technology, makes them attractive candidates for the realization of solid state qubits. The corresponding near perfect isolation from their environment, however, renders the individual addressing and coupling of such qubits a major challenge on the way towards a spin quantum computer based on ionized donors. We show that the application of strain to the silicon host crystal leads to shifts of the nuclear spin resonance frequencies of $^{75}$As$^+$ due to the nuclear quadrupole interaction with crystal fields. This shift can be larger than the resonance linewidth already for modest strains, as we demonstrate by electrically detected electron nuclear double resonance (ED ENDOR) measurements on arsenic donors in strained silicon. We discuss how quadrupole interactions could allow for the individual addressing of ionized nuclear spins by mechanical tuning of their resonance frequency and, possibly, permit the elastic coupling of nuclear spin qubits to a mechanical resonator. [Preview Abstract] |
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