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CATEGORIES:Lecture
DESCRIPTION:New platforms for quantum sensing and quantum computing\n\nThe 
 nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescenc
 e and long spin coherence times under ambient conditions\, enabling applica
 tions in quantum information processing and sensing. NV centers near the su
 rface can have strong interactions with external materials and spins\, enab
 ling new forms of nanoscale spectroscopy. However\, NV spin coherence degra
 des within 100 nanometers of the surface\, suggesting that diamond surfaces
  are plagued with ubiquitous defects. I will describe our recent efforts to
  correlate direct materials characterization with single spin measurements 
 to devise methods to stabilize highly coherent NV centers within nanometers
  of the surface. We deploy these coherent shallow NV centers for a new nano
 scale sensing technique\, whereby we use covariance measurements of two or 
 more NV centers to measure two-point magnetic field correlators. \nOur appr
 oach for correlating surface spectroscopy techniques with single qubit meas
 urements to realize directed improvements is generally applicable to many s
 ystems. Separately\, I will describe our recent efforts to tackle noise and
  microwave losses in superconducting qubits. Building large\, useful quantu
 m systems based on transmon qubits will require significant improvements in
  qubit relaxation and coherence times\, which are orders of magnitude short
 er than limits imposed by bulk properties of the constituent materials. Thi
 s indicates that loss likely originates from uncontrolled surfaces\, interf
 aces\, and contaminants. Previous efforts to improve qubit lifetimes have f
 ocused primarily on designs that minimize contributions from surfaces. Howe
 ver\, significant improvements in the lifetime of 2D transmon qubits have r
 emained elusive for several years. We have recently fabricated 2D transmon 
 qubits that have both lifetimes and coherence times exceeding 0.3 milliseco
 nds by using tantalum as the material in the capacitor. Following this disc
 overy\, we have parametrized the remaining sources of loss in state-of-the-
 art devices using systematic measurements of the dependence of loss on temp
 erature\, power\, and geometry. This parametrization\, complemented by dire
 ct materials characterization\, allows for rational\, directed improvement 
 of superconducting qubits. We have used this playbook to tackle the dominan
 t sources of loss and noise to realize 2D transmons with coherence times ex
 ceeding 1 millisecond and lifetimes up to 1.68 milliseconds. Because we hav
 e improved the underlying material system without alteration to the qubit a
 rchitecture\, these qubits are readily translated to existing control schem
 es\, and we demonstrate single qubit gates with 99.994% fidelity.
DTEND:20250423T210000Z
DTSTAMP:20260315T104509Z
DTSTART:20250423T200000Z
GEO:42.335064;-71.168846
LOCATION:Higgins Hall\, 310
SEQUENCE:0
SUMMARY:Physics Colloquium: Nathalie de Leon\, Princeton University
UID:tag:localist.com\,2008:EventInstance_48834894420341
URL:https://events.bc.edu/event/physics-colloquium-nathalie-de-leon-princet
 on-university
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