Harvard University Department of Physics

Efficient Topological Materials Discovery using Symmetry Indicators

pie chart of topological materials statistics

Researchers have now shown that the computation of symmetry indicators for any crystalline symmetry setting can readily be integrated into standard first-principle calculations...

Harvard Science Book Talk: David Reich (Feb 27 @6:00PM)

Photo of Prof. David Reich and cover of the book "Who We Are and How We Got Here"

In this lecture, Prof. Reich will discuss his new book, Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past.

Congratulations to David Morin and Jacob Barandes!

David Morin and Jacob Barandes named Co-Directors of Undergraduate and Graduate Studies, respectively...

UPCOMING EVENTS

Today

Hannes Pilcher, Harvard University
Start: 09:00am - End: 10:00am
- From many-body physics to quantum information with atomic and photonic systems
  
  Quantum many-body systems have unique properties that give rise to fascinating phenomena and potential applications, ranging from exotic phases of matter to new paradigms for information processing and communication. Quantum optical systems allow to engineer such quantum many-body systems in a controlled, bottom-up approach. This enables new ways to create and probe states of matter but also poses new theoretical challenges for describing them. I will illustrate this in my talk on a few examples.
  
  I will first discuss the many-body quantum phenomena associated with arrays of trapped Rydberg atoms. This includes the equilibrium quantum phase diagram and the quantum critical behavior, as well as novel non-equilibrium phenomena such as quantum many-body scars.
  
  Moreover, I will show how these systems can be used to naturally encode combinatorial optimization problems and realize quantum optimization algorithms.
  
  In the last part of my talk I will discuss new approaches to quantum information processing with photonic systems. In particular, I will introduce delayed quantum feedback as a novel tool to create highly entangled photon states, and show that it enables universal quantum computation already with a single quantum emitter.
- 09:00am
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MATH:
Start: 03:00pm - End: 03:00pm
- Organizer: Mathematical Picture Language Seminar
- 03:00pm
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CUA Seminar: Dr. Christophe Salomon (Ecole Normale Supérieure)
Start: 04:00pm - End: 05:30pm
- Dual Bose Fermi Superfluids: surprises in the ultracold worldWe will describe the first production and study of a novel quantum system, a mixture of Bose and Fermi superfluids. Such a mixture had long been sought in liquid helium where superfluidity was only achieved separately in bosonic 4He and fermionic 3He. Using dilute quantum gases where interactions can be tuned, we have produced a Bose-Fermi mixture where both species are in the superfluid state [1]. By exciting center of mass oscillations of the mixture we probe the equation of state of the strongly correlated Fermi gas. The superfluid counterflow exhibits very small damping below a certain critical velocity [2]. This velocity is surprisingly high and is compared to a recent theoretical prediction [3]. Finally the lifetime of the Bose-Fermi mixture is governed by a very simple formula involving the fermionic two-body contact [4].[1] Igor Ferrier-Barbut, Marion Delehaye, Sebastien Laurent, Andrew T. Grier, Matthieu Pierce, Benno S. Rem, Frédéric Chevy, Christophe Salomon, A Mixture of Bose and Fermi Superfluids, Science 345, 1035, (2014)[2] M. Delehaye, S. Laurent, I. Ferrier-Barbut, S. Jin, F. Chevy, and C. Salomon, Critical Velocity and Dissipation of an ultracold Bose-Fermi Counterflow, Phys. Rev. Lett., 115, 265303 (2015).[3] Y. Castin, I. Ferrier-Barbut, and C. Salomon, The Landau critical velocity for a particle in a Fermi superﬂuid, Comptes Rendus Physique, 16, 241 (2015). [4] S. Laurent, M. Pierce, M. Delehaye, T. Yefsah, F. Chevy, C. Salomon, Connecting few-body inelastic decay to quantum correlations in a many-body system : a weakly coupled impurity in a resonant Fermi gas, Phys. Rev. Lett., 118, 103403 (2017)
- 04:00pm
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Tomorrow

Tim Atherton - Tufts
Start: 06:00pm - End: 07:30pm
- 06:00pm
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Thursday, February 21st

Andrew Potter, University of Texas
Start: 09:00am - End: 10:00am
- "Universal principles of quantum dynamics: an entanglement perspective"
  
  abstract: Experimental advances in AMO systems from trapped atoms, ions, and molecules, to superconducting and spin qubits provide a powerful tool-kit for exploring the quantum dynamics of interacting quantum many-body systems. Despite being well-isolated from their environment, such systems often have many sources of internal dissipation that cause raid scrambling quantum information and eventual relaxation to an effective thermal equilibrium. Surprisingly, while common, thermalization is not inevitable.
  
  This talk will explore two key developments in understanding the universal principles of athermal quantum dynamics through the lens of quantum information and entanglement:
  1) I will first investigate how introducing random disorder causes thermalization and statistical mechanics to break down via a many-body localization (MBL) phase transition. A real-space renormalization group approach enables a controlled numerical calculation of the universal properties of this transition, and reveals an unconventional scaling features that depart from the traditional structure of traditional thermal and quantum critical points.
  2) Next, I will describe how time-periodic (Floquet) driving of MBL systems can produce topological dynamical phases with sharply quantized dynamics. These phases offer robust ways of manipulating entanglement and protecting quantum information that are exponentially insensitive to control errors.
- 09:00am
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ITAMP Lunch Seminar
Start: 12:00pm - End: 01:00pm
- Speaker: Shmuel Bialy (CFA)
- 12:00pm
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Lucas Hackl (Max Planck), hosted by Eugene Demler
Start: 03:00pm - End: 04:00pm
- Title: Geometric tangent plane methods and the Bose-Hubbard model
  
  Abstract: The paradigmatic Bose-Hubbard model describes interacting bosons which can be experimentally realized with ultracold atoms in optical lattices. In this talk, I will focus on the superfluid phase and introduce geometric methods to find approximate ground states and quasi particle excitations. For the variational class of Gaussian states, we can systematically extend Bogoliubov theory and compute quasi particle excitations, life times and spectral functions. To our surprise, we find a bound state below the continuum. Depending on the interaction strength, the dispersion relation of the bound state enters the continuum for larger momentum. I will conclude with discussing observable effects and how we can test if this finding is physical.
- 03:00pm
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Monday, February 25th

Monika Schleier-Smith - Stanford University
Start: 04:15pm - End: 05:15pm
- Choreographing Quantum Spin Dynamics with Light
  
  The power of quantum information lies in its capacity to be non-local, encoded in correlations among two, three, or many entangled particles. Yet our ability to produce, understand, and exploit such correlations is hampered by the fact that the interactions between particles and necessarily local. I will report on experiments in which we engineer effectively non-local interactions among cold atoms by letting photons serve as messengers conveying information between them. The combination of optically programmable interactions with imaging of spin dynamics opens new opportunities in areas ranging from quantum-enhanced sensing to quantum simulation. As an illustrative example, I will touch on prospects for building and probing toy models for information scrambling in black holes.
- 04:15pm
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Tuesday, February 26th

Alex Ruichao Ma, University of Chicago
Start: 09:00am - End: 10:00am
- "Exploring Synthetic Quantum Matter in Superconducting Circuits"
  
  abstract: Understanding strongly correlated materials is an outstanding challenge in modern physics. Synthetic quantum matter, tailor-made in the lab as clean, tunable and easy to probe quantum simulators, can help us gain insights into such strongly correlated matter, and explore new parameter regimes with no natural counterpart.
  
  In this talk, I will show how we create and explore quantum materials made of light, specifically microwave photons trapped in superconducting circuits. We develop a new approach for preparing many-body phases, where engineered dissipation is used as a resource to protect the fragile quantum states against intrinsic losses. We apply it to our system, a strongly interacting Bose-Hubbard lattice, and realize a dissipatively stabilized Mott insulator of photons. The dynamics of thermalization towards the Mott phase is probed using lattice-site- and time- resolved microscopy.
  
  Our experiments establish superconducting circuits as a powerful platform for studying quantum materials, and open many future possibilities including the exploration of strongly interacting topological phases, quantum thermodynamics in coherent or driven-dissipative settings, and hybrid quantum systems with exotic couplings.
- 09:00am
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MATH:
Start: 03:00pm - End: 03:00pm
- Organizer: Mathematical Picture Language Seminar
- 03:00pm
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CUA Seminar: Prof. Ben Lev (Stanford University)
Start: 04:00pm - End: 05:30pm
- Many-body cavity QED with multimode resonatorsWe will present our first experiments involving multimode cavity QED, wherein the cavity-mediated atom-atom interaction is dramatically modified compared to that in a single-mode cavity. We demonstrate the engineering of strong, tunable-range, and sign-changing photon-mediated interactions between atoms and between atomic spins. A mechanism for photon-mediated interactions based on the Gouy phases of the cavity modes is introduced and demonstrated. Such interactions can be exploited for the creation of unusual quantum many-body phases. Other results include the observation of a ‘spinor density-wave polariton’ condensate and cavity-assisted dynamical spin-orbit coupling. Together, these results pave the way for future experimental access to nontrivial quantum phases and transitions in driven-dissipative quantum systems, synthetic dynamical gauge fields, and the ability to study nonequilibrium spin glasses and quantum neural networks.
- 04:00pm
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