Harvard University Department of Physics

A Quantum Science Initiative at Harvard

Quantum science—the physics and engineering of the world at sub-microscopic scales—got a boost today as Harvard formally announced an initiative that will combine basic and applied research into the realm of the very small, as well as foster collaborations...

Sending Spin Waves into an Insulating 2D Magnet

Quantum Hall ferromagnets are among the purest magnets in the world — and one of the most difficult to study. These 2D magnets can only be made in temperatures less than a degree above absolute zero...

Origin of Mott Insulating Behavior and Superconductivity in Twisted Bilayer Graphene

A new theory describes how both insulating and superconducting behavior arises from sheets of graphene stacked and twisted at a particular "magic" angle.

UPCOMING EVENTS

Tomorrow

No Squishy Physics - Happy Thanks Giving
Start: 06:00pm - End: 07:30pm
- 06:00pm
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Monday, November 26th

Professor Matthew Reece, Harvard University
Start: 04:15pm - End: 05:15pm
- “Fundamental Physics from Underground to the Sky”
  
  The Large Hadron Collider’s discovery of the Higgs boson has only sharpened some of the biggest puzzles in fundamental physics. Why is gravity so dramatically weak compared to the other fundamental forces of nature? What is the dark matter that is far more prevalent in our universe than normal matter? Finding the answers to such questions is likely to require us to sharpen our theoretical tools and to study experimental signals from cosmology and astrophysics that lie far afield from traditional particle experiment. I will highlight some recent research aiming to strengthen connections among particle physics, astrophysics, and cosmology.
- 04:15pm
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Tuesday, November 27th

CUA Seminar: Achim Rosch (University of Cologne)
Start: 04:00pm - End: 05:30pm
- Driven quantum systems: ratchets, pumps and equilibrationUltracold atoms provide unique opportunities to study many-body quantum systems out of equilibrium. We first investigate theoretically how an interacting quantum system reaches thermal equilibrium. While a few scattering events rapidly establish a local equilibrium, the ultimate bottleneck for equilibration is the building up of a characteristic pattern of thermal fluctuations. Using the one-dimensional bosonic Hubbard model as an example, we show that this leads to pronounced hydrodynamic long-time trials and power-law instead of exponential relaxation. Second, we study how one can use periodically driven systems to control interacting systems focusing on cases where the periodic driving can imprint currents on the system.
- 04:00pm
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Wednesday, November 28th

HQOC/ITAMP joint talk -Peter Lodahl (University of Copenhagen)
Start: 04:00pm - End: 05:30pm
- Quantum-Information Processing with Solid-State Single-Photon Emitters
  
  Semiconductor quantum dots have improved their optical performance dramatically in recent years, and today a clear pathway is laid out for constructing a deterministic and coherent photon-emitter interface by embedding quantum dots in photonic nanostructures [1]. Such an interface can be employed as an on- demand single-photon source for quantum-information applications, but more generally enables single-photon nonlinearities and deterministic quantum gates [2]. We will review the recent experimental progress on quantum dots coupled to nanophotonic waveguides and cavities as a mean to engineer light-matter interaction. We discuss current status on efficiency, coherence [3,4] and brightness [5], as well as the fundamental limits of photon indistinguishability [6,7]. Various potential quantum-information processing protocols are put forward that exploits the deterministic photon-emitter interface for single-photon nonlinear optics and spin physics. Finally, the experimental demonstration of a photonic switched
  controlled by a single spin coupled to a waveguide is discussed [8].
  
  References
  [1] Lodahl et al., Rev. Mod. Phys. 87, 347 (2015).
  [2] Lodahl, Quantum Science and Technology 3, 013001 (2018).
  [3] Kirsanske et al., Phys. Rev. B 96, 165306 (2017).
  [4] Thyrrestrup et al., Nano Letters 18, 1801 (2018)
  [5] Daveau et al., Optica 4, 178 (2017).
  [6] Tighineanu et al., Phys. Rev. Lett. 120, 257401 (2018).
  [7] Dreessen et al., Quantum Science and Technology 4, 015003 (2019).
  [8] Javadi et al., Nature Nanotechnology 13, 398 (2018).
- 04:00pm
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Yoav Green - Harvard School of Public Health
Start: 06:00pm - End: 07:30pm
- 06:00pm
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Thursday, November 29th

CMP Seminar: Cristian Batista (University of Tennessee), hosted by Ashvin Vishwanath
Start: 12:00pm - End: 01:00pm
- Title: Dynamical structure factor of the triangular Heisenberg model
  
  Abstract: Motivated by recent experiments in Ba3Co2Sb2O9, I will derive the zero-temperature dynamical structure factor S(q,ω) of the triangular lattice Heisenberg model using a Schwinger Boson approach that includes the Gaussian fluctuations (1/N correction) of the saddle point solution. While the ground state of this model exhibits a well-known 120-degree magnetic ordering, the excitation spectrum revealed by S(q,ω) has a strong quantum character, which is not captured by low-order 1/S expansions. The low-energy magnons consist of two-spinon bound states confined by the gauge fluctuations of the auxiliary fields. In addition, the continuum of high-energy spinon modes extends up to three times the single-magnon bandwidth. I will compare these results against previous numerical calculations and neutron scattering data on Ba3Co2Sb2O9. In addition, I will show that the linear spin wave result is recovered in the S→∞ limit.
  
  * Work done in collaboration with E. A. Ghioldi, M. G. Gonzales, S-S. Zhang, Y. Kamiya, L. Manuel and A. E. Trumper [Phys. Rev. B 98, 184403 (20018)]
- 12:00pm
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ITAMP Lunch Seminar
Start: 12:00pm - End: 01:00pm
- Speaker: Vedika Khemani
- 12:00pm
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