Physics Department Colloquia

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Events During the Week of January 21st through January 28th, 2024

Monday, January 22nd, 2024

No events scheduled

Tuesday, January 23rd, 2024

No events scheduled

Wednesday, January 24th, 2024

No events scheduled

Thursday, January 25th, 2024

Semiconductor qubits on the move: low power and high-fidelity quantum gates
Time: 3:30 pm - 5:00 pm
Place: Discovery Building, DeLuca Forum
Speaker: Menno Veldhorst, QuTech – Delft University of Technology

Loss and DiVincenzo proposed in 1998 that quantum dots define excellent building blocks for a fault-tolerant quantum computer. By confining individual electrons in quantum dots, qubits can be defined on the electron spin states, and controlled using electrical signals. Two decades of intensive research on spin qubits in quantum dots has resulted in many proof-of-principle demonstrations. However, a realization of the original proposal remained elusive. In their proposal, Loss and DiVincenzo envisaged that if the magnetic orientation varies between quantum dots, hopping an electron between the two quantum dots would allow for fast and efficient qubit logic. Practically, it has remained too challenging to create such variations in the magnetic orientation. Here, we demonstrate that changes in the spin quantization axis can be realized, by making use of spin qubits in germanium. This is achieved by exploiting the strong spin-orbit interaction in germanium, which can cause orientations that differ by tens of degrees. In addition, we establish hopping of an electron between two quantum dots, where the spin remains coherent over effective length scales beyond a millimeter. This allows to realize qubit fidelities up to 99.97% and two-qubit gates of 99.3%. We then apply our findings to larger quantum circuits to explore pathways toward fault-tolerant quantum computation.

This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Yinqi Chen (PhD student Maxim Vavilov group) titled "Voltage-Controlled Quantum Entanglement in Superconductor-Semiconductor Devices". The invited presentation starts at 4pm.

Host: Mark Eriksson
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Friday, January 26th, 2024

Gravitational-wave astronomy with LIGO-Virgo-KAGRA
Time: 3:30 pm - 4:30 pm
Place: 2241 Chamberlin Hall
Speaker: Patrick Brady, University of Wisconsin-Milwaukee
Abstract: Brady will describe the current state of ground-based, gravitational-wave astronomy and the prospects for the future. He will present highlights from LIGO-Virgo-KAGRA observations including recent findings on compact object mergers. Gravitational waves from black-hole-binary mergers are now being detected about twice per week and astronomers are eagerly awaiting the next multi-messenger event. Over the next decade, a sequence of upgrades will more than double the amplitude sensitivity of the most sensitive gravitational-wave detectors and increase the rate of compact binary detections by about a factor of ten. Brady will discuss how the improved signal-to-noise ratio will also enable unprecedented measurements of masses, spins, and other properties of black holes and neutron stars in binary systems. The upgrades may also bring the discovery of other gravitational-wave sources. The talk will end with a discussion of future directions for ground-based gravitational-wave astronomy, highlighting the opportunities for multimessenger astronomy in the early 2030s and how operations of the current detector network can dovetail with operations of next-generation facilities such as Cosmic Explorer and Einstein Telescope.
Host: Justin Vandenbroucke
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