Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G39: Semiconductor Qubits IVFocus Recordings Available
|
Hide Abstracts |
Sponsoring Units: DQI DCMP Chair: Xinxin Cai, Rochester Room: McCormick Place W-196A |
Tuesday, March 15, 2022 11:30AM - 12:06PM |
G39.00001: Multi-qubit quantum logic operations with ion-implanted donor spins in silicon Invited Speaker: Andrea Morello Among semiconductor qubits, the electron and nuclear spins of donors in silicon play a special role for their conceptual simplicity (a 31P donor in silicon is similar to hydrogen in vacuum) and their exceptional coherence times [1] and 1-qubit gate fidelities [2]. Here I will present experimental progress on multi-qubit logic operations with donor spins, which point to several credible pathways for scalability using ion-implanted donors in MOS-compatible devices. The current state of the art is a hybrid electron-nuclear 3-qubit processor [3], where two 31P nuclear spin qubits are coupled to the same electron. The shared electron enables a geometric nuclear two-qubit CZ gate, which we perform with 99.37% average fidelity. NMR single-qubit gates reach fidelities up to 99.95%, and state preparation and measurement are performed with 98.95% fidelity. These three metrics show how close this system is to operating at fault-tolerance thresholds. Further, we entangle the two nuclei with the electron to prepare a 3-qubit GHZ state with 92.5% fidelity. Electron-nuclear entanglement unlocks the ability to connect nuclear qubits via the electrons, for instance using exchange interactions [4]. We have operated a weakly (~10 MHz) exchange-coupled 31P donor pair as a 2-qubit electron system, with native CROT gates performed by resonant microwaves. Gate fidelity benchmarks are underway and will be reported at the Meeting. On the engineering side, we have demonstrated the ability to implant single donors in silicon with confidence up to 99.85% [5]. This striking result identifies ion implantation as a scalable and accurate manufacturing strategy for spin-based quantum computers in silicon. |
Tuesday, March 15, 2022 12:06PM - 12:18PM |
G39.00002: Characterizing noise sources of spin qubit devices with the anisotropy in relaxation and dephasing times Yujun Choi, Robert J Joynt Spin qubits in semiconductor quantum dots devices are one of the promising platforms for building a quantum computer. Understanding the noise that degrades their performance is a central issue. Thus we wish to have experiments that can distinguish and characterize charge noise, evanescent-wave Johnson noise, and noise from nuclear spins and phonons. To do this, we can use qubits that act as natural noise sensors and one would like to make them as sensitive as possible to the tensor structure of electric and magnetic noise. We propose that rotating the external magnetic field can give much information about the noise tensor, which in turn sheds light on the noise mechanisms. We compute the anisotropy in the relaxation time and the dephasing time of the qubit for these mechanisms and shows how to use this information to better understand the nature and position of the noise sources in present-day spin-qubit devices. |
Tuesday, March 15, 2022 12:18PM - 12:30PM |
G39.00003: Interacting Two-Level Systems as a Source of 1/f Noise in Semiconductor Quantum Dot Qubits Dan Mickelsen, Herve M Carruzzo, Clare C Yu Charge noise in quantum dots has been attributed one or two fluctuators coupled to each quantum dot. To explain why the observed charge noise has a 1/f spectrum rather than the expected Lorentzian, we propose a model in which a quantum dots are coupled to one or two fluctuators that have electric dipole moments. These fluctuators are in turn coupled elastically to a bath of fluctuating elastic dipoles that cause changes in the energy of the electric dipole fluctuators, resulting in 1/f charge noise. We simulate this model with Ising spin glasses in both 2D and 3D. We determine the magnetization noise spectrum of a few chosen Ising spins, each of which we imagine to be coupled to a quantum dot. The noise exponents are computed from the noise power spectra observed at three types of spins where the magnitude of the local field is small (|hlocal ≈ 0|), medium (|hlocal ≈ 2|), and large (|hlocal ≈ 4|). The ranges of the noise exponents are consistent with those found experimentally. The noise exponents depend on the local field and tend to increase with the magnitude of the local field. |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G39.00004: Closed-shell formation in few-electron Si quantum dots Ekmel Ercan, Susan N Coppersmith, Mark G Friesen, Christopher R Anderson, Mark F Gyure Multielectron quantum dots in Si have desirable properties as qubit platforms. For example, it has been shown that single-electron spins sitting above a closed shell of electrons can be electrically driven more effectively [1]. On the other hand, closed shells are also expected to be sensitive to the strength of electron-electron (e-e) interactions. Moreover, in Si quantum dots, the valley degree of freedom and disorder-induced valley-orbit coupling play critical roles in shell spectroscopy and qubit operations. In this talk, we theoretically investigate these effects by combining tight-binding calculations (to incorporate valley physics) and full-configuration interactions (to incorporate e-e interactions), with the goal of achieving a quantitative understanding of the underlying physics and rationally designing and manipulating qubits. |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G39.00005: Simulations of Spin Qubit Dynamics Made Simple Mykyta Onizhuk, Giulia Galli The coherence of solid-state spin qubits is limited by their magnetic environment, consisting of electron and nuclear spins (see, e.g. [1]). To facilitate and enhance first-principles calculations of qubits’ coherence, we developed PyCCE, an open-source Python library for simulating the dynamics of spin qubits in a spin bath using the cluster-correlation expansion (CCE) method. PyCCE includes modules to generate realistic spin baths, employing coupling parameters computed from first principles with electronic structure codes (see, e.g. [2]), and enables the user to run simulations with either the conventional or generalized CCE method. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G39.00006: Phonon-Induced Gate Infidelities in Semiconducting Spin Qubits Matthew Brooks, Rex O Lundgren, Charles Tahan Spin-spin exchange interactions between semiconductor quantum dot spin qubits provide fast single and/or two-qubit gates, depending on the qubits encoding. During exchange, at finite temperatures, coupling of the qubits to the surrounding phonon bath may cause errors in the resulting gate. Here, the fidelities of operations with semiconductor double quantum dot spin qubits coupled to a phonon bath are considered. |
Tuesday, March 15, 2022 1:06PM - 1:18PM |
G39.00007: Observation of anomalous T1 relaxation during exchange in Si/SiGe spin qubits Edwin Acuna Encoded triple-quantum-dot qubits are promising for quantum information processing as they rely solely on the exchange interaction for qubit control. Here, we report on spin population relaxation observed during electron-electron exchange but not detected in coherent exchange oscillation measurements. This relaxation, which is distinct from well-known dephasing from charge and magnetic hyperfine noise, has been observed impacting randomized benchmarking fidelity. We characterize this relaxation time, denoted T1J, using a variety of experiments, including the full-permutation dynamical decoupling technique [1] where this decoherence process may manifest as leakage from the qubit subspace. We also demonstrate experiments which highlight exchange biases that extend this timescale, and discuss possible sources for this relaxation. We expect T1J processes may be relevant to the performance of other spin qubit technologies that utilize the exchange interaction. |
Tuesday, March 15, 2022 1:18PM - 1:30PM |
G39.00008: Two-Level-Fluctuators as a source of 1/f noise and quantum gate errors in spin qubits Mohamed K Shehata, George Simion, Fahd Mohiyaddin, Roy Li, Asser El Sayed, Nard D Stuyck, Clement Godfrin, Massimo Mongillo, Pol Van Dorpe, Iuliana P Radu, Bogdan Govoreanu Electrons confined in gate defined quantum dots are promising candidates for qubit implementations. Long coherence times have been achieved by migrating to isotopically purified Silicon platforms in which nuclear hyperfine interactions are minimized. However, charge noise still remains a limiting factor for the spin qubits' coherence and quantum gate fidelities. Noise spectral densities measured via charge sensors and decoherence behaviour of qubits show 1/f -like trends, which are characteristic of charge noise. In this work we gain insights on the charge noise profile by simulating the electrostatic fluctuations introduced by different Two-Level-Fluctuators (TLFs). The result is then compared to experimentally measured noise spectral densities measured by Single Electron Transistors (SET). We further assess the sensitivity of one- and two- qubit quantum gates to the charge fluctuations introduced by the aforementioned TLFs based on combining electrostatic models with configuration interaction and quantum dynamics calculations. The microscopic treatment of individual TLFs presented here offers an insight on the nature of the charge noise sources in addition to enabling realistic incorporation of charge noise in quantum mechanical models of spin qubit devices. |
Tuesday, March 15, 2022 1:30PM - 1:42PM |
G39.00009: Coherent control of electron spin qubits in silicon using a global field Ensar Vahapoglu, James Slack-Smith, Ross C. C. Leon, Wee Han Lim, Fay E Hudson, Tom Day, Jesus D Cifuentes Pardo, Tuomo I Tanttu, Chih-Hwan Yang, Andre Saraiva, Michael Thewalt, Nikolay (N.V.) Abrosimov, Hans-Joachim Pohl, Arne Laucht, Andrew S Dzurak, Jarryd J Pla Spin-based silicon quantum electronic circuits offer a scalable platform for quantum computation, combining the manufacturability of semiconductor devices with the long coherence times afforded by spins in silicon. Advancing from current few-qubit devices to silicon quantum processors with upwards of a million qubits, as required for fault-tolerant operation, presents several unique challenges, one of the most demanding being the ability to deliver microwave signals for large-scale qubit control. Here we demonstrate a potential solution to this problem by using a 3D dielectric resonator to broadcast a global microwave signal across a quantum nanoelectronic circuit. Critically, this technique utilizes only a single microwave source and is capable of delivering control signals to millions of qubits simultaneously. We first show that the global field can be used to perform spin resonance of single electrons confined in a natural silicon double quantum dot device [1]. Then, by switching to an isotopically purified device, we report coherent Rabi oscillations of single electron spin qubits using a global magnetic field generated off-chip [2]. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer. |
Tuesday, March 15, 2022 1:42PM - 1:54PM |
G39.00010: 3-Dimensional Tuning of an Atomically Defined Silicon Tunnel Junction Matthew B Donnelly, Joris G Keizer, Yousun Chung, Michelle Y Simmons An important requirement for quantum information processors is the in-situ tunability of tunnelling within the device for optimising high fidelity single shot spin read-out and for tunable coupling of the exchange interaction energy. The large energy level separation for atom qubits in silicon resulting from the strong Coulomb confinement of the donor atoms is well suited for qubit operation but creates challenges for device tunability. In this paper we address control of the simplest tunnelling element in atomic-scale devices – the tunnel junction, a barrier between two phosphorus doped conducting electrodes on one atomic plane. We demonstrate that we can tune the conductance of this critical element by using a vertically separated top-gate aligned with ~5nm precision to the junction. We show that by incorporating this 3D epitaxial top-gate with increased capacitive coupling compared to in-plane gates we can tune the conductance of the tunnel junction by an order of magnitude (equating to a change in the tunnel barrier height from ~0 to 190 meV). By combining multiple gated junctions in series we extend our 3D gating technology to implement transistor-like operations based on electron tunnelling, and simple nanoscale AND and OR logic circuits. |
Tuesday, March 15, 2022 1:54PM - 2:06PM |
G39.00011: Correlations and valley phenomena in strained graphene superlattices Antonio L Manesco, Jose Lado, Gabrielle Weber, Elton José Figueiredo de Carvalho In this work, we explore two platforms where strained graphene superlattices were observed: spontaneously buckled graphene, and suspended graphene on engineered substrates. In the former, emerging flat bands have been recently shown to realize correlated states analogous to those observed in twisted graphene multilayers. We show that electronic correlations leads to a competition between antiferromagnetic and charge density wave instabilities. Moreover, the charge density wave state has a topologically non-trivial electronic structure, leading to a coexistent quantum valley Hall insulating state. In a similar fashion, the antiferromagnetic phase realizes a spin-polarized quantum valley-Hall insulating state. To study the effects of strain in suspended graphene superlattices, we perform molecular dynamics simulations. The computed strain field is used to obtain an effective Hamiltonian and the resulting pseudo magnetic field. We use this platform to investigate the presence of defects such as of wrinkles in the electronic structure. Under the quantum Hall regime, we show the existence of valley-polarized chiral edge states. Our results put forward strained graphene superlattices as tunable platforms to investigate valley topology. |
Tuesday, March 15, 2022 2:06PM - 2:18PM |
G39.00012: Particle-hole symmetry protects spin-valley blockade in graphene quantum dots Luca Banszerus, Samuel Moeller, Eike Icking, Kenji Watanabe, Takashi Taniguchi, Fabian Hassler, Christian Volk, Christoph Stampfer Particle-hole symmetry plays an important role for the characterization of topological phases in solid-state systems. Graphene is a textbook example of a gapless particle-hole symmetric system, where topological phases can be understood by studying ways to open a gap by breaking symmetries [1]. An important example is the intrinsic Kane-Mele spin-orbit gap of graphene, which renders graphene a topological insulator in a quantum-spin Hall phase [2]. |
Tuesday, March 15, 2022 2:18PM - 2:30PM |
G39.00013: Pulsed-gate spectroscopy on single-electron quantum dots in bilayer graphene Katrin Hecker, Luca Banszerus, Samuel Möller, Eike Icking, Kenji Watanabe, Christian Volk, Christoph Stampfer, Takashi Taniguchi Thanks to its weak spin-orbit coupling and low nuclear spin density bilayer graphene (BLG) promises long spin relaxation and coherence times, making this material a potentially interesting platform for spin-based solid state quantum computation [1]. Although the electrostatic confinement of single electrons in BLG quantum dot (QD) devices has been demonstrated and their single particle spectrum has been studied in detail [2,3], their relaxation dynamics remain so far mostly unexplored [4]. Here, we report on measurements of the spin relaxation times (T1) of single-electron spin states in a BLG QD. Using pulsed-gate spectroscopy, we extract T1 times exceeding 200μs at out-of-plane magnetic fields below 2T. The measured values for T1 show a strong dependence on the spin splitting and increase by about two orders of magnitude when decreasing the magnetic field from 2-3 T, suggesting that T1 could be significantly larger at low magnetic fields.
[1] B. Trauzettel et al., Nat. Phys. 3, 192 (2007). [2] M. Eich et al., Phys. Rev. X 8, 031023 (2018). [3] A. Kurzmann et al., Phys. Rev. Lett. 123, 026803 (2019). [4] L. Banszerus et al., Phys. Rev. B 103, L081404 (2021). |
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