Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F29: Semiconductor Qubits  Spin Qubit Readout IIFocus Live

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Sponsoring Units: DQI Chair: Edward Chen, IBM Research  Almaden 
Tuesday, March 16, 2021 11:30AM  12:06PM Live 
F29.00001: Microsecond singlespin readout in semiconductors in the “strongresponse” regime Invited Speaker: Daniel Keith Faulttolerant quantum computation requires qubit measurements to be both high fidelity and fast to minimise errors on measured and idling qubits and reduce the integrated measurement noise over the course of an experiment. Towards this goal, we demonstrate singleshot readout of semiconductor singlespin qubits with 97% fidelity in 1.5 μs. In particular, we show that we can engineer donorbased singleelectron transistors (SETs) in silicon with atomic precision to measure single spins much faster than the spin decoherence times in isotopically purified silicon (270 μs). By designing the SET to have a large capacitive coupling between the SET and target charge, we can optimally operate in the “strongresponse” regime to ensure maximal signal contrast. We demonstrate singlecharge detection with a signaltonoise ratio (SNR) of 12.7 at 10 MHz bandwidth, corresponding to a SET charge sensitivity (integration time for SNR=2) of 2.5 ns. We present a theory of the shotnoise sensitivity limit for the strongresponse regime which predicts that the present sensitivity is about one order of magnitude above the shotnoise limit. By reducing cold amplification noise to reach the shotnoise limit, it should be theoretically possible to achieve highfidelity, singleshot readout of an electron spin in silicon with a total readout time of approximately 36 ns. 
Tuesday, March 16, 2021 12:06PM  12:18PM Live 
F29.00002: Remote Capacitive Sensing in TwoDimensional QuantumDot Arrays Jingyu Duan, Michael A. Fogarty, James Williams, Louis HUTIN, Maud Vinet, John J. L. Morton

Tuesday, March 16, 2021 12:18PM  12:30PM Live 
F29.00003: Adiabatic conversion for qubit readout: Optimal pulse shapes and dephasing Felix Fehse, Michel PioroLadriere, Bill Coish Adiabatic conversion schemes are commonly used to 
Tuesday, March 16, 2021 12:30PM  12:42PM Live 
F29.00004: Automatic, adaptive and sparse acquisition of Coulombblockade boundaries in quantumdot arrays (Part 2) Bertram Brovang, Torbjørn Rasmussen, Anasua Chatterjee, Oswin Krause, Ferdinand Kuemmeth

Tuesday, March 16, 2021 12:42PM  12:54PM Live 
F29.00005: Parametric Amplification in a CMOS Quantum Dot coupled to a Microwave Cavity Laurence Cochrane, Theodor Lundberg, David J. Ibberson, Lisa A. Ibberson, Louis HUTIN, Maud Vinet, Ashwin A. Seshia, M Fernando GonzalezZalba Parametric amplification through pumping a nonlinear or variable reactive element of a resonator can approach quantumlimited noise performance. Josephson junction parametric amplifiers (JPAs) based on a nonlinear inductance have been instrumental in enabling rapid, high fidelity readout of superconducting qubits and, recently, semiconductor quantum dots (QDs). 
Tuesday, March 16, 2021 12:54PM  1:06PM Live 
F29.00006: SubGHz Josephson parametric amplifiers for the readout of sensors and quantum dots Visa Vesterinen, Slawomir Simbierowicz, Robab Najafi Jabdaraghi, Leif Grönberg, Janne Lehtinen, Mika Prunnila, Joonas Govenius We present our latest experimental results on subGHz Josephson parametric amplifiers (JPAs) fabricated with our Nb/AlAlO_{x}/Nb junction process [1]. The early generation of our fluxdriven reflectiontype JPA has found applications in the radiofrequency readout of bolometers [2], as well as quantum dots [3]. We have recently addressed bandwidth limitations by engineering a partially reconfigurable impedance transformer. With a bandwidth of 10 MHz at 20 dB gain at 600 MHz, the improved JPA is in line with the requirements of fast readout schemes for, e.g., semiconductor quantum dots. In addition, we have experimented with a variant where unwanted nonlinearities are suppressed by alternating the dipolar orientation of superconducting nonlinear asymmetric inductive elements (SNAILs) in an array. 
Tuesday, March 16, 2021 1:06PM  1:18PM Live 
F29.00007: Nuclear spin readout in a cavitycoupled silicon double quantum dot Jonas Mielke, Jason Petta, Guido Burkard Nuclear spins show long coherence times and are well isolated from the environment, which are properties making them promising for quantum information applications. However, these same qualities make the readout of nuclear spin qubits challenging. Here, we present a method for nuclear spin readout by probing the transmission of a microwave resonator. We consider the flopping mode spin qubit [1,2] formed by a single electron in a silicon double quantum dot subjected to a homogeneous magnetic field and a transverse magnetic field gradient. This qubit interacts with a microwave resonator via the electric dipole coupling allowing for strong spin photon coupling [3,4]. In our scenario, the electron spin interacts with a ^{31}P defect nuclear spin via the hyperfine interaction. Our theoretical investigation demonstrates a ^{31}P nuclear spin state dependent change of the cavity transmission that could be resolved in experiments and used to readout the state of the nuclear spin. 
Tuesday, March 16, 2021 1:18PM  1:30PM Live 
F29.00008: Quantum simulations of manybody physics using nuclearspin qubits in diamond Joe Randall, Conor Bradley, Floris van der Gronden, Mohamed Abobeih, Tim Hugo Taminiau Interacting nuclear spins in diamond are a promising new platform for simulating manybody physics phenomena, due to their naturally realised spinspin interactions combined with highfidelity control and selective readout. Recently, we demonstrated the 3D imaging of a cluster of 27 coupled nuclear spins using a nitrogen vacancy (NV) centre in diamond [1], as well as a fully connected 10qubit register formed of 9 nuclear spins combined with the NV centre electron spin [2]. 
Tuesday, March 16, 2021 1:30PM  1:42PM Live 
F29.00009: Quantum information processing with highdensity diamond nitrogenvacancy centers in strain and magnetic fields. Zhujing Xu, ZhangQi Yin, Qinkai Han, Tongcang Li The longsought scalable quantum information processor is a critical challenge since it requires long coherence time as well as full control and readout of every single qubit. Here we propose methods to use closely spaced diamond nitrogenvacancy (NV) centers for realizing quantum information processing and quantum computing. The NV centers are coupled with their adjacent color centers by spinspin interactions. By applying a strain gradient, the position of each NV center is encoded and hence more than 100 NV centers can be read out individually due to the narrow linewidths and the dispersive distributions of the optical transition frequencies. At the same time, the individual control of the spin states can be realized by a positiondependent magnetic field. The strain and magnetic field gradient provide the flexibility to independently manipulate and selectively couple the electron spins. We also present a universal set of quantum gates with high fidelity combined utilizing optimal control methods for this solidstate system. 
Tuesday, March 16, 2021 1:42PM  1:54PM Live 
F29.00010: Entanglement between two intrinsically coherenceprotected spin qubits Hans Bartling, Mohamed Abobeih, Benjamin Pingault, Maarten J Degen, Sjoerd Loenen, Conor Bradley, Joe Randall, Tim Hugo Taminiau Understanding and protecting the coherence of individual quantum systems is a central challenge in quantum science and technology. A variety of methods to protect coherence have been demonstrated, including clock states, dynamical decoupling, quantum error correction, isotopic purification, and decoherenceprotected subspaces. Here we introduce a new type of longlived quantum system: a pair consisting of two identical coupled nuclear spins. These spin pairs naturally combine clock states with decoherenceprotected subspaces making them intrinsically robust to external perturbations. We study three carbon13 nuclear spin pairs and realize highfidelity control and singleshot readout using a single NV center in their vicinity. We demonstrate a long inhomogeneous dephasing time, T2* = 113(18) seconds. Finally, we demonstrate complete control over these qubits by preparing an entangled state of two spin pairs through projective quantum parity measurements. The longlived spin pairs demonstrated here are naturally abundant in diamond and other solidstate systems, and provide new opportunities for quantum bits, quantum networks and precision measurements. 
Tuesday, March 16, 2021 1:54PM  2:06PM Live 
F29.00011: Inductive detection and amplification of spin echoes using a superconducting parametric amplifier Wyatt Vine, Mykhailo Savytskyi, Daniel Parker, Brett Johnson, Jeffrey McCallum, Andrea Morello, Jarryd Pla In recent years, the cQED toolkit has been successfully applied to push the boundary of measurement sensitivity in electron spin resonance (ESR) spectroscopy [1,2,3]. In particular, the adoption of Josephson Parametric Amplifiers has allowed the noise in ESR spectrometers to approach the quantum limit. Here we report the use of a degenerate parametric amplifier (DPA) to perform insitu amplification of spin echo signals in pulsed ESR measurements of ^{209}Bi donors in Silicon. Unlike previous work, the spins here have a direct inductive coupling to the DPA, which is constructed from a quarterwavelength resonator in a thin NbTiN film. The DPA serves as both the ESR cavity and firststage amplifier for spin echo signals. We show that the device is capable of operating in a magnetic field of 250 mT and greatly enhances the SNR of pulsed ESR measurements. 
Tuesday, March 16, 2021 2:06PM  2:18PM Live 
F29.00012: Automatic, adaptive and sparse acquisition of Coulombblockade boundaries in quantumdot arrays (Part 1) Anasua Chatterjee, Fabio Ansaloni, Bertram Brovang, Torbjørn Rasmussen, Oswin Krause, Ferdinand Kuemmeth For spinbased quantum processors, controlled transitions in quantumdot arrays between one ground state to other competing ground states are of significant operational significance, as these allow movements of quantum information within otherwise empty arrays (singleelectron shuttling), or wave function overlap of one spin with another (coherent Heisenberg spin exchange). Even for small arrays, dense raster scans in controlvoltage space become impractical, due to the large number of measurements needed to sample the highdimensional gatevoltage cube, and the comparatively little information (Coulomb diamond boundaries) one gains. 
Tuesday, March 16, 2021 2:18PM  2:30PM On Demand 
F29.00013: Robust photonmediated entangling gates between singleelectron quantum dots Ada Warren, Utkan Güngördü, Jason Kestner, Edwin Barnes, Sophia Economou Recent experimental and theoretical work on singleelectron spin qubits in silicon has opened the possibility of realizing longdistance entangling gates mediated by microwave photons. Currently proposed iSWAP gates, however, require qubits to be tuned to resonance with one another, and have limited fidelity due to charge noise. We present here a novel, photonmediated crossresonance gate which requires no resonant tuning, as well as a nested entangling gate sequence capable of suppressing gate errors due to quasistatic charge noise. 
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