Events

Spring 2021
University of Wisconsin, Madison, Department of Physics

QUANTUM CONTROL OF SPINS IN SILICON

Quantum computing is based on the manipulation of two-level quantum systems, or qubits. In most approaches to quantum computing, qubits are as much as possible isolated from their environment in order to minimize the loss of qubit phase coherence. The use of nuclear spins as qubits is a well-known realization of this approach. In a radically different approach, quantum computing is also possible for strongly coupled multi-electron spin 1/2 systems, as realized in silicon-based devices. In this talk I will present both a historical overview of how quantum manipulation in silicon has developed, as well as the latest results from both our group at Wisconsin and from around the world. I will discuss our recent demonstration of coherent manipulation of eight different microwave-frequency resonances in a single silicon quantum dot, which starts to glimpse the future prospect of spin qubits being controlled using the types of powerful tools developed for controlling atoms by the AMO community over many decades. I will end with a brief discussion of how silicon fits into the broad quantum science and technology ecosystem, which is growing at an astounding rate. This article in Physics Today discusses closely related material: Quantum computing with semiconductor spins. Bio: Mark A. Eriksson is the John Bardeen Professor of Physics at the University of Wisconsin-Madison. He received a B.S. with honors in physics and mathematics in 1992 from the University of Wisconsin-Madison and an A.M. (1994) and Ph.D. (1997) in physics from Harvard University. His Ph.D. thesis demonstrated the first cryogenic scanned-gate measurements of a semiconductor nanostructure. He was a postdoctoral member of technical staff at Bell Laboratories from 1997-1999, where he studied ultra-low-density electron systems. Eriksson joined the faculty of the Department of Physics at UW-Madison in 1999. His research has focused on quantum computing, semiconductor quantum dots, and nanoscience. With collaborators he demonstrated the first quantum dot in silicon/silicon-germanium occupied by an individual electron and performed the first experiments to demonstrate the quantum dot hybrid qubit. Eriksson currently leads a multi-university team focused on the development of spin qubits in gate-defined silicon quantum dots. A goal of this work is to enable quantum computers, which manipulate information coherently, to be built using many of the materials and fabrication methods that are the foundation of modern, classical integrated circuits. Eriksson was elected fellow of the American Physical Society in 2012 and of the American Association for the Advancement of Science in 2015. All lectures are via Zoom

University at Buffalo, Department of Physics

SPIN QUBITS IN SI: COHERENCE AND CONTROL

Electron spin qubits in Si are promising candidates as building blocks toward future scalable quantum computers. Tremendous progress has been made in the past decade in demonstrating the exceptional coherence properties of spins confined in quantum dots and donors. However, studies of high-fidelity manipulation of spin qubits have encountered numerous problems as well: for donors, the small Bohr radius makes donor electrons hard to locate and control; for quantum dots, especially ones in Si/SiGe heterostructures, small valley splitting makes spin detection based on spin blockade difficult to realize. In this talk I discuss our recent work on spin manipulation and decoherence in Si quantum dots. I will first show that the complex valley-orbit coupling in a Si quantum dot can be significantly impacted by the atomistic scale features of an interface. The different valley mixing angles across a double dot would remove all valley selection rules in electron tunneling, and cause significant modification to the two-electron exchange coupling. On the decoherence front, I will discuss our recent study of spin relaxation in a Si quantum dot under the influence of a micromagnet that allows electrical control of single spins in Si. We show that the field gradient generated by a micromagnet amounts to an artificial spin-orbit interaction. However, unlike intrinsic spin-orbit coupling, which causes only spin relaxation, a micromagnet would cause both spin relaxation and pure dephasing, and generate a longitudinal effective field that could potentially be used for spin manipulation. We thank support by US ARO. Short Bio: Xuedong Hu is a physics professor at the University at Buffalo, the State University of New York. He received his PhD degree in condensed matter theory from University of Michigan in 1996, supervised by Franco Nori. He was introduced to the field of solid state quantum information processing in 1998 as a postdoc in Sankar Das Sarma’s group at the University of Maryland. His recent research focus is on spin qubits in silicon.

Monday–Friday, March 15–19, 2021, virtual APS March Meeting 2021


March 2, 2021, virtual
University of Colorado @ Boulder, JILA

METROLOGY WITH OPTICAL TWEEZER ARRAYS OF NEUTRAL ATOMS

Quantum science with neutral atoms has seen great advances in the past two decades. Many of these advances follow from the development of new techniques for cooling, trapping, and controlling atomic samples. As one example, the technique of optical tweezer trapping of neutral atom arrays has been a powerful tool for quantum simulation and quantum information, because it enables control and detection of individual atoms with switchable interactions. In this talk, I will describe ongoing work at JILA where we have explored a new direction for the optical tweezer platform: metrology. I will report our recent progress towards combining scalability and quantum coherence in a tweezer-based optical atomic clock platform, and our efforts towards using quantum information concepts and many-body dynamics to create entangled states that enhance metrological performance. Much of this technology is based in the use of tweezer-trapping of a new family of atoms, alkaline-earth atoms — I will discuss the broader outlook of this direction and new pursuits on the horizon. Recorded Video Link Tweezing a New Kind of Atomic Clock Bio: Dr. Adam Kaufman is an associate JILA fellow and assistant professor adjoint at CU Boulder. He did his PhD at JILA, studying few-body quantum mechanics of atoms in optical tweezers. Afterwards, as a postdoctoral fellow at Harvard, he investigated the dynamics of entanglement in thermalizing many-body systems and other Bose-Hubbard phenomena. In 2017, he moved back to JILA where he has continued working in the field of quantum science with neutral atoms. He is a winner of the prestigious APS DAMOP thesis prize in 2016, and he pioneered the research on atomic clocks based on optical tweezers.

February 25-26, 2021, virtual NSF Workshop on Quantum Engineering Education

Fall 2020

 

Colorado School of Mines
Denver University

AN INTRODUCTION TO OPTICAL VORTICES AND TOPOLOGICAL FLUIDS OF LIGHT

 Hydrodynamic whirlpools have fascinated scientists for centuries, seeking to understand their individual structure, stability, and the ways in which they interact with one another. Who hasn’t marveled at tornadoes or watched as soap bubbles get sucked into the vortex of a bathtub drain? To reduce ideas to their essence, such fluid vortices are often considered in a two-dimensional setting where they amount to current swirling around a singularity. These, in turn, bear a striking resemblance to cross-sections of optical vortices that can be created with lasers, but with the propagation axis now treated as time. The vortex center is a then a dark spot about which the phase of light rotates like a barber shop sign. Such engineered light can therefore be interpreted as a two-dimensional, compressible fluid, and the vortices it harbors exhibit all sorts of odd and potentially useful behavior. For instance, optical vortices can attract, repel, scatter, and even annihilate one another. Even more intriguing, these two-dimensional topological objects have a lot in common with the macroscopic quantum states of Bose-Einstein condensates and fractional quantum Hall systems. Pairs can even be used in Bell tests to demonstrate lack of local realism. This motivates a serious consideration of optical vortices as quantum objects that might be harnessed in emerging quantum information technologies. With these deeper issues in mind, our colloquium lecture is intended to serve as an introduction to optical vortices and their classical few-body dynamics. We tag-team an experimentalist and a theorist to provide a fuller perspective of what makes this form of light so interesting.

University of New South Wales

QUANTUM-COHERENT SILICON ELECTRONICS

Silicon is an attractive materials platform for developing large-scale quantum computers because of its compatibility with classical silicon electronics and its potential for scalability. This talk will discuss qubits made from quantum dots with multiple electrons in silicon/silicon-germanium heterostructures. These qubits can be manipulated on nanosecond time scales, and their coherence can be extended greatly by appropriate manipulation protocols. They can be tuned so that additional quantum resonances appear that can be driven coherently, which we show is consistent with effects arising form strong electron-electron interactions. Thus, these multi-electron qubits are interesting both as building blocks for quantum computers and as testbeds for investigating strongly interacting electrons. Recorded Video Link

August 13, 2020, virtual 6th Front Range Advanced Magnetics Symposium (FRAMS)


May 26, 2020, virtual Open Quantum Frontier Institute Virtual Workshop: Quantum Education 2nd workshop of the Open Quantum Frontier Institute


April 13-14, 2020 Dr. Zaira Nazario IBM Dr. Nazario will present on quantum computing. CANCELLED


February 28, 2020, 2-3 pm in CoorsTek 282 Fernando Sols Universidad Complutense de Madrid Departamento de Física de Materiales

Protected cat states in a driven superfluid boson gas

We investigate the behavior of a one-dimensional Bose-Hubbard gas in both a ring and a hard-wall box, whose kinetic energy is made to oscillate with zero time average, which suppresses first-order particle hopping while allowing even higher-order processes [1]. At a critical value of the driving, the system passes from a Mott insulator to an exotic superfluid phase. The system in the ring has similarities to the Richardson pairing model which can be exploited to understand key features of the interacting boson problem [2]. The superfluid ground state is a macroscopic quantum superposition, or cat state, of two many-body states characterized by the preferential occupation of opposite momentum eigenstates. Interactions give rise to a reduction (or modified depletion) cloud that is common to both macroscopically distinct states. Symmetry arguments permit a precise identification of the two orthonormal many-body branches forming the ground state. In the ring, the system is sensitive to variations of the effective flux but in such a way that the macroscopic superposition is preserved. We discuss other physical aspects that contribute to protect the catlike nature of the ground state. [1] G. Pieplow, F. Sols, C. E. Creffield, New J. Phys. 20, 073045 (2018). [2] G. Pieplow, C. E. Creffield, F. Sols, Phys. Rev. Research 1, 033013 (2019).

February 21-22, 2020 at the Colorado School of Mines in Golden, CO Open Quantum Frontier Institute 1st workshop of the Open Quantum Frontier Institute


September 16-17, 2019 in Alexandria, VA Quantum Simulators: Architectures and Opportunities US NSF-supported workshop See more on the Quantum Engineering @ Mines Workshops page link.