Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M32: Invited Session: Semiconductor Qubits |
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Sponsoring Units: GQI DCMP Chair: Malcolm Carroll, Sandia National Laboratories Room: 708-712 |
Wednesday, March 5, 2014 11:15AM - 11:51AM |
M32.00001: Hybrid Circuit QED with Double Quantum Dots Invited Speaker: Jason Petta Cavity quantum electrodynamics explores quantum optics at the most basic level of a single photon interacting with a single atom. We have been able to explore cavity QED in a condensed matter system by placing a double quantum dot (DQD) inside of a high quality factor microwave cavity. Our results show that measurements of the cavity field are sensitive to charge and spin dynamics in the DQD.\footnote{M. D. Schroer, M. Jung, K. D. Petersson, and J. R. Petta, ``Radio frequency charge parity meter,'' Phys. Rev. Lett. \textbf{109}, 166804 (2012).}$^,$\footnote{K. D. Petersson, L. W. McFaul, M. D. Schroer, M. Jung, J. M. Taylor, A. A. Houck, and J. R. Petta,``Circuit quantum electrodynamics with a spin qubit,'' Nature (London) \textbf{490}, 380 (2012).} We can explore non-equilibrium physics by applying a finite source-drain bias across the DQD, which results in sequential tunneling. Remarkably, we observe a gain as large as 15 in the cavity transmission when the DQD energy level detuning is matched to the cavity frequency. These results will be discussed in the context of single atom lasing.\footnote{Y.-Y. Liu, K. D. Petersson, J. Stehlik, J. Taylor, and J. R. Petta, ``Photon emission from a cavity-coupled double quantum dot,'' (in preparation).} I will also describe recent progress towards reaching the strong-coupling limit in cavity-coupled Si DQDs. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:27PM |
M32.00002: High Visibility Coherent Oscillations in a Si/SiGe Quantum Dot Hybrid Qubit Invited Speaker: Mark Eriksson We discuss measurement and manipulation of a quantum dot hybrid qubit [1] formed in a Si/SiGe heterostructure. X-rotations on the Bloch sphere are performed by pulsing a gate voltage so that the detuning of a double quantum dot makes the (1,2) and (2,1) occupation ground states degenerate [2]. The resulting rotation rate is approximately 5 GHz and reveals an experimentally measured visibilty greater than 80 percent. Z-rotations on the Bloch sphere are performed by pulsing a gate voltage away from the (1,2)-(2,1) degeneracy point, resulting in oscillations at a rate of approximately 10 GHz and measured visibility greater than 85 percent. The T2* time at this detuning is greater than 15 ns, many times longer than the 100 ps gate operation time. In part because of the large ratio between the gate time and the dephasing time, improvements in the pulses used in the experiment are expected to enhance the visibility beyond that reported here and to enable high fidelity quantum gates. This work was supported in part by ARO (W911NF-12-0607), NSF (DMR-1206915), and the United States Department of Defense. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressly or implied, of the US Government. This work was performed in collaboration with Dohun Kim, Zhan Shi, C. B. Simmons, D. R. Ward, J. R. Prance, Xian Wu, R. T. Mohr, Teck Seng Koh, John King Gamble, Ryan Foote, D. E. Savage, M. G. Lagally, Mark Friesen, and S. N. Coppersmith. \\[4pt] [1] Z. Shi, C. B. Simmons, J. R. Prance, John King Gamble, Teck Seng Koh, Yun-Pil Shim, Xuedong Hu, D. E. Savage, M. G. Lagally, M. A. Eriksson, Mark Friesen, and S. N. Coppersmith, Phys. Rev. Lett. 108, 140503 (2012).\\[0pt] [2] Teck Seng Koh, John King Gamble, Mark Friesen, M. A. Eriksson, and S. N. Coppersmith, Phys. Rev. Lett. 109, 250503 (2012). [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 1:03PM |
M32.00003: Quantum gate-set tomography Invited Speaker: Robin Blume-Kohout Quantum information technology is built on (1) physical qubits and (2) precise, accurate quantum logic gates that transform their states. Developing quantum logic gates requires good characterization -- both in the development phase, where we need to identify a device's flaws so as to fix them, and in the production phase, where we need to make sure that the device works within specs and predict residual error rates and types. This task falls to quantum state and process tomography. But until recently, protocols for tomography relied on a pre-existing and perfectly calibrated reference frame comprising the measurements (and, for process tomography, input states) used to characterize the device. In practice, these measurements are neither independent nor perfectly known -- they are usually implemented via exactly the same gates that we are trying to characterize! In the past year, several partial solutions to this self-consistency problem have been proposed. I will present a framework (gate set tomography, or GST) that addresses and resolves this problem, by self-consistently characterizing an entire set of quantum logic gates on a black-box quantum device. In particular, it contains an explicit closed-form protocol for linear-inversion gate set tomography (LGST), which is immune to both calibration error and technical pathologies like local maxima of the likelihood (which plagued earlier methods). GST also demonstrates significant (multiple orders of magnitude) improvements in efficiency over standard tomography by using data derived from long sequences of gates (much like randomized benchmarking). GST has now been applied to qubit devices in multiple technologies. I will present and discuss results of GST experiments in technologies including a single trapped-ion qubit and a silicon quantum dot qubit. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:39PM |
M32.00004: Quantum Computing in Silicon with Donor Electron Spins Invited Speaker: Michelle Simmons Extremely long electron and nuclear spin coherence times have recently been demonstrated in isotopically pure Si-28 [1-3] making silicon one of the most promising semiconductor materials for spin based quantum information. The two level spin state of single electrons bound to shallow phosphorus donors in silicon in particular provide well defined, reproducible qubits [4] and represent a promising system for a scalable quantum computer in silicon. An important challenge in these systems is the realisation of an architecture, where we can position donors within a crystalline environment with approx. 20-50nm separation, individually address each donor, manipulate the electron spins using ESR techniques and read-out their spin states. We have developed a unique fabrication strategy for a scalable quantum computer in silicon using scanning tunneling microscope hydrogen lithography to precisely position individual P donors in a Si crystal [5] aligned with nanoscale precision to local control gates [6] necessary to initialize, manipulate, and read-out the spin states [7]. During this talk I will focus on demonstrating electronic transport characteristics and single-shot spin read-out of precisely-positioned P donors in Si. Additionally I will report on our recent progress in performing single spin rotations by locally applying oscillating magnetic fields and initial characterization of transport devices with two and three single donors. The challenges of scaling up to practical 2D architectures will also be discussed. \\[4pt] [1] M. Steger et al., Science 336, 1280 (2012).\\[0pt] [2] A.M. Tyryshkin et al., Nature Materials 11, 143 (2012). \\[0pt] [3] K. Saeedi et al., Science 342, 130 (2013).\\[0pt] [4] B.E. Kane, Nature 393, 133 (1998).\\[0pt] [5] M. Fuechsle et al., Nature Nanotechnology 7, 242 (2012).\\[0pt] [6] B. Weber et al., Science 335, 6064 (2012).\\[0pt] [7] H. Buch et al., Nature Communications 4, 2017 (2011). [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 2:15PM |
M32.00005: Entanglement between two singlet-triplet qubits Invited Speaker: Amir Yacoby |
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