Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q37: Focus Session: Semiconductor Qubits - Hybrid Systems and Electrons Floating on Liquid Helium |
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Sponsoring Units: GQI Chair: Steve Lyon, Princeton University Room: 212A |
Wednesday, March 4, 2015 2:30PM - 3:06PM |
Q37.00001: Semiconductor double quantum dot micromaser Invited Speaker: Yinyu Liu The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Circuit quantum electrodynamics (cQED) allows strong coupling between microwave photons and a solid-state quantum device. Photon emission has recently been observed from a cavity coupled double quantum dot.\footnote{ Y. Y. Liu, K. D. Petersson, J. Stehlik, J. M. Taylor, and J. R. Petta, Phys. Rev. Lett. \textbf{113}, 036801 (2014).} Here we demonstrate a two atom maser that is created by coupling two double quantum dots (DQDs) to a microwave cavity. Charge transport through the DQDs results in a gain as large as 1000 in the cavity transmission. With no cavity drive, the free emission spectrum has a linewidth of 34 kHz, which corresponds to a coherence length of 3 km. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q37.00002: Superconducting Nanowire Resonators for Coupling to Spin Qubits at High Magnetic Fields Nodar Samkharadze, Pasquale Scarlino, Alessandro Bruno, Leonardo Di Carlo, Lieven Vandersypen High quality factor superconducting microwave resonators are a powerful tool for quantum information processing, as they provide a promising interface between different solid state quantum systems. One of the challenges in coupling of superconducting resonators with spin systems is the typically poor performance of these resonators in high magnetic fields. We present a novel design of microwave resonators based on NbTiN nanowires, which retain intrinsic quality factors above 10$^5$ while subjected to in-plane magnetic fields up to 1.2T. Moreover, due to their high characteristic impedance, these nanowire resonators are expected to develop 10 times higher vacuum fluctuation voltages than the standard coplanar waveguide resonators, making them well suited for spin-orbit interaction mediated strong coupling to spin qubits. [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q37.00003: Phonon Assisted Gain in a Semiconductor Double Quantum Dot Maser Michael Gullans, Y.-Y. Liu, J. Stehlik, C. Eichler, J. R. Petta, J. M. Taylor We develop a microscopic model for a double quantum dot (DQD) maser. In characterizing the gain of this device we find that, in addition to the direct stimulated emission of photons, there is a large contribution from transitions that involve the simultaneous emission of a photon and a phonon. This phonon assisted process controls the lasing transition because it dominates the gain in the region of large population inversion. These theoretical results are compared to experiment. The broadband nature of this phonon assisted process implies that the maser operation is robust against charge noise and fabrication imperfections. In addition, due to the sharp threshold behavior of the lasing transition, this work indicates that the maser can serve as an extremely sensitive probe of the mesoscopic environment of the DQD. [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q37.00004: Cavity-coupled double-quantum dot at finite bias: analogy with lasers and beyond Ovidiu Cotlet, Manas Kulkarni, Hakan Tureci We present [1] a theoretical and experimental study of photonic and electronic transport properties of a voltage biased InAs semiconductor double quantum dot (DQD) that is dipole-coupled to a superconducting transmission line resonator. We obtain the Master equation for the reduced density matrix of the coupled system of cavity photons and DQD electrons accounting systematically for both the presence of phonons and the effect of leads at finite voltage bias. We subsequently derive analytical expressions for transmission, phase response, photon number and the non-equilibrium steady state electron current. We show that the coupled system under finite bias realizes an unconventional version of a single-atom laser and analyze the spectrum and the statistics of the photon flux leaving the cavity. In the transmission mode, the system behaves as a saturable single-atom amplifier for the incoming photon flux. Finally, we show that the back action of the photon emission on the steady-state current can be substantial. Our analytical results are compared to exact Master equation results establishing regimes of validity of various analytical models. We compare our findings to available experimental measurements.\\[4pt] [1] M. Kulkarni, O. Cotlet, H. E. Tureci, Phys. Rev. B 90, 125402 (2014) [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q37.00005: Coherent coupling of a single spin to microwave cavity photons Jeremie Viennot, Matthieu Dartiailh, Audrey Cottet, Takis Kontos The main goal in the recent development of hybrid circuit quantum electrodynamics with quantum dots is to find efficient means to couple single spins to cavity photons. So far though, only the coupling of photons to the charge degree of freedom could be demonstrated. Here, we demonstrate a large and coherent spin photon coupling in a cQED architecture at the single spin level. Our scheme relies on the use of a non collinear spin valve which realizes an artificial spin orbit interaction. Thanks to that interaction we are able to couple electronic states which are sensitive to the external magnetic field to cavity photons. We observe a hysteretic evolution of the phase of the microwave signal as a function of the external magnetic field, stemming from the spin valve behavior of the device. This demonstrates an efficient spin/photon coupling and illustrates a new method for manipulating the quantum mechanical spin degree of freedom. Our findings can be used to scale up spin quantum bit architectures. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q37.00006: High quality factor superconducting resonators on Si/SiGe semiconductor heterostructures Jeffrey Cady, Xiao Mi, J.R. Petta The circuit quantum electrodynamics architecture may allow for the generation of entanglement between spatially separated spin qubits [1]. This approach has introduced the challenge of fabricating high quality factor superconducting resonators on multilayered semiconductor substrates. Here we present electric field simulations which show that 30\% of the resonator electric field resides in the 675$\mu$m thick Si substrate on which the Si/SiGe heterostructure is grown, 55\% resides in the 3 $\mu$m thick SiGe relaxed buffer and 300 nm of Si$_{0.7}$Ge$_{0.3}$ grown above the relaxed buffer, and 15\% resides in the remaining Si/SiGe heterostructure. We evaluate the performance of Nb coplanar waveguide resonators fabricated on top of a strained Si/SiGe quantum well at 4.2 K and 10 mK. The tested resonators exhibit a high quality factor despite the presence of an accumulated two-dimensional electron gas beneath the resonator center pin.\\[4pt] [1] K. D. Petersson \textit{et al.}, Nature {\bf490}, 380-383 (2012). [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q37.00007: Phosphorus donors in silicon in the strong coupling regime C. W. Zollitsch, K. M\"{u}ller, M. S. Brandt, R. Gross, H. Huebl In the field of quantum information storage spin ensembles are promising candidates due to their long coherence times. In particular, phosphorus dopants in silicon are very attractive candidates with their record breaking electron and nuclear spin coherence times exceeding 0.5~s [1] and 39~min [2], respectively. Their combination with microwave resonators in the strong coupling regime lays the basis of controlled information transfer between subsystems, i.e. quantum state storage. Here, we report on the observation of a superconducting coplanar niobium microwave resonator and an ensemble of phosphorus donors in an isotopically enriched $^{28}$Si host lattice entering the strong coupling regime. By low-power microwave transmission spectroscopy we find at a temperature of 50 mK the characteristic double peak signature. Studying the coupling strength $g_{eff}$ up to 3.5~K shows quantitative agreement with the expected $g_{eff}=g_0\sqrt{N}$ scaling, being proportional to the square root of the thermal spin polarization. The crossover from the strong coupling regime to the weak coupling regime is observed at 200~mK allowing for further investigation of the two regimes. [1] J. T. Muhonen \textit{et al.}, Nat. Nano. (2014) [2] K. Saeedi \textit{et al.}, Sci. 342, 830 (2013) [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q37.00008: Electron Spin Resonance Spectroscopy of Bismuth donors in Silicon using a Parametric Amplifier Yuimaru Kubo, Audrey Bienfait, Michael Stern, Denis Vion, Daniel Esteve, Patrice Bertet, Jarryd Pla, Cheuk Chi Lo, John Morton, Christoph Weis, Thomas Schenkel, Michael Thewalt Bismuth donor spins in Silicon are well suited to implement a quantum memory for superconducting qubits [1], owing to their long coherence times and large hyperfine interaction leading to a zero-field splitting of 7.35GHz [2]. We report low-field electron-spin resonance spectroscopies of ensembles of Bismuth spins with a concentration of 5 10$^{16}$cm$^{-3}$ in an isotopically purified $^{28}$Si sample at 10 mK, at which the electronic spin is expected to be fully polarized. The spectrometer consists of a planar aluminium superconducting resonator patterned on top of the substrate, with a quality factor of 10$^{5}$. The signal coming from the spins is amplified using a Josephson Parametric Amplifier [3]. Hahn-echo coherence times up to 10 ms are observed. \\[4pt] [1] B. Julsgaard, C. Grezes, P. Bertet, K. Moelmer, Phys. Rev. Lett. 110, 250503 (2013).\\[0pt][2] G. Wolfowicz et al., Nature nanotechnology 8, 561 (2013).\\[0pt][3] X. Zhou et al., Phys. Rev. B 89, 214517 (2014). [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q37.00009: Entanglement of Two, Three, and Four Quantum Dots in Hybrid Quantum Dot/Plasmonic Systems Matthew Otten, Raman Shah, Norbert Scherer, Misun Min, Matthew Pelton, Stephen Gray We use cavity quantum electrodynamics to study systems composed of two, three, and four two-state quantum dots in proximity to a plasmonic system such as a metal nanoparticle or an array of metal nanoparticles. We find that significant essential (all dot) entanglement, as measured by concurrence, in the two and four quantum dot cases is possible. At present the three quantum dot case lacks an easily applied measure of entanglement, but multiple bipartite entanglements are demonstrated. Moreover, we show that one can induce entanglement in two and three quantum dot systems starting from the ground state by use of pulsed excitations. These results represent a promising advance for the eventual use of quantum dots, coupled to one another through a dissipative structure such as a plasmonic system, in quantum computation. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q37.00010: Ripplonic Lamb shift for electrons on liquid helium Denis Konstantinov, Kono Kimitoshi, Michael Lea, Mark Dykman We resolve a long-standing controversy regarding the electrons on the surface of helium and their coupling to capillary waves, ripplons. The direct two-ripplon coupling to short-wavelength ripplons is strong. It leads to a strong power-law ultraviolet divergence of the shifts of the electron energy levels and to a high energy relaxation rate of the excited states. We use the Bethe-type approach to show that one-ripplon processes, taken to the higher order of the perturbation theory, compensate the divergence of the level shifts. The resulting shifts, which are ripplonic analogs of the Lamb shift, are small. The transition frequencies display characteristic temperature dependence. The calculation of this dependence with no adjustable parameters for transitions between the two lowest subbands of motion along the surface is in good agreement with our experimental data. We also show that one-ripplon processes renormalize the energy relaxation rate, which for highly excited electron states is determined by two-ripplon emission. As a result, energy relaxation is much slower than the lowest-order theory predicts. This is important for applications of electrons on helium in quantum information. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q37.00011: Isolating Electrons on the Surface of Superfluid Helium Maika Takita, C. Spencer Nichols, Stephen Lyon Electrons on helium have been suggested as promising mobile spin qubits. Electrons floating on the surface of superfluid helium can be transferred extremely efficiently in narrow channels with underlying gates. The channels are filled with superfluid helium by capillary action and electrons on the surface can be clocked over a billion pixels in a 3-phase charge coupled device (CCD) without any detectable transfer errors. To use electrons as qubits, we need to reliably obtain a single electron per pixel. We demonstrate an electron turnstile operating across 78 parallel channels for isolating electrons. First, electrons are accumulated over wide 2.3um channels and clocked using the CCD gates into the narrow 0.8um wide turnstile regions. When large packets of electrons are clocked from the wide channels through the narrow regions, the number of electrons per pixel decreases. Using the narrow underlying gates in the turnstile region, the electron packets are repeatedly split. We find a plateau in the electron signal as a function of the applied gate voltages indicating a quantized number of electrons per pixel in each of the 78 parallel channels. [Preview Abstract] |
Wednesday, March 4, 2015 5:06PM - 5:18PM |
Q37.00012: Modeling Strongly Interacting Electrons on Helium Coupled to a Microwave Resonator Ge Yang, David G. Rees, Leonidas Ocola, David Czaplewski, Gerwin Koolstra, David McKay, David I. Schuster Electrons on helium is a unique two-dimensional electron gas system formed at the interface of a quantum liquid (superfluid helium) and vacuum. If single electrons on helium can be isolated, the motional and spin states could form the building blocks for hybrid quantum computing [1,2]. However, to trap single electrons we must start from a 2-dimensional gas of many electrons, which is a strongly interacting classical gas. In our experiment, we trap mesoscopic samples of electrons in a micron-sized trap at the end of a centimeter-long quarter wavelength microwave cavity, and interrogate the system via the change in the microwave resonance frequency. Here, we will present a simple numeric model that we developed to understand the coupled cavity-electron on helium system in a micron-sized trap, and insights towards building a single electron quantum dot. [1] S. Lyon, Phys. Rev. A. 74, 5 (2006) [2] D.I. Schuster, et al. Phys. Rev. Lett. 105, 040503 (2010) [Preview Abstract] |
Wednesday, March 4, 2015 5:18PM - 5:30PM |
Q37.00013: Entanglement dynamics of capacitively coupled spin qubits in the presence of stray inductance Michael Wolfe, Shawna Chisholm, Jason Kestner A pair of spin qubits formed by electrons confined in a pair of double quantum dots can be entangled at distances on the order of microns via a floating metallic top gate that mediates capacitive coupling [1]. The double-well biases, and hence the coupling through the top gate, can be controlled through voltage leads connected to an arbitrary waveform generator. We theoretically examine how the entanglement dynamics of the system are affected by inductance of the coupling element when the biases are driven at high frequencies. We numerically simulate the von Neumann entropy of the reduced density matrix as a function of time in various parameter regimes. In particular, we examine the behavior when the qubits are driven near the resonance frequency of the coupling element. \\[4pt] [1] L. Trifunovic et al., Phys. Rev. X 2, 011006 (2012). [Preview Abstract] |
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