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Applied Physics / Physics Colloquium

Q-Farm Quantum Seminar Series presents "Surprises from Time Crystals"

Topic: 
Surprises from Time Crystals
Abstract / Description: 

Time crystals are new states of matter that only exist in an out-of-equilibrium setting. I will review the state of this rapidly evolving field, focusing in particular on some of the remarkable properties of this phase, and the surprises coming out of its study. I will provide a detailed overview of existing experiments, with a view towards identifying the ingredients needed for an unambiguous observation of this phase in the future.

Date and Time: 
Wednesday, January 29, 2020 - 12:00pm
Venue: 
Hansen Physics & Astrophysics Building, 102/103

Applied Physics/Physics Colloquium: Quantum Optical Control of Levitated Solids: a novel probe for the gravity-quantum interface

Topic: 
Quantum Optical Control of Levitated Solids: a novel probe for the gravity-quantum interface
Abstract / Description: 

The increasing level of control over motional quantum states of massive, solid-state mechanical devices opens the door to a hitherto unexplored parameter regime of macroscopic quantum physics. I will report on our recent progress towards controlling levitated solids in the quantum regime. I will discuss the prospects of using these systems for fundamental tests of physics, including the interface between quantum and gravitational physics.


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, March 3, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Dark Matter halos from parametric resonance and their signatures"

Topic: 
Dark Matter halos from parametric resonance and their signatures
Abstract / Description: 

While there is undisputed evidence for Dark Matter, its nature and properties remain one of the biggest questions of our time. What is Dark Matter (DM)? How is it produced? Does it have interactions other than gravitational? In this talk, I will describe how a large class of bosonic particles can account for the DM of the Cosmos. These particles can be much lighter than those of the Standard Model with Compton wavelengths that are bigger than the size of our solar system or smaller than a millimeter. In the presence of attractive self-interactions, there is a parametric resonance effect in the early universe that can cause growth of structure at small scales, an effect so dramatic that can cause structures to collapse well before matter-radiation equality. The signatures of this effect span several experiments and orders of magnitude in parameter space. When the DM boson is heavy, the dense DM halos can alter the optimal search strategies in direct detection experiments. When the DM boson is light, these halos may leave their imprint in searches for dark matter substructure, primordial gravitational waves and alter the star formation history of the universe.


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, February 25, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Fracton – elasticity duality"

Topic: 
Fracton – elasticity duality
Abstract / Description: 

I will discuss a recent discovery that elasticity theory of a two-dimensional quantum crystal is dual to a fracton tensor and to a coupled-vector gauge theories, thereby providing a concrete realization of the so-called "fracton quantum order". The disclinations and dislocations respectively map onto charges and dipoles of these gauge theories. The fractionalized mobility of fractons matches the constrained dynamics of crystal's topological defects. These dualities lead to predictions of fractonic phases, and phase transitions to their descendants, that are duals of the commensurate crystal, supersolid, smectic, and hexatic liquid crystals. Extensions of this duality to generalized elasticity theories provide a route to discovery of new fractonic models and their potential experimental realizations.


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, February 18, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Quantum Science with Tweezer Arrays"

Topic: 
Quantum Science with Tweezer Arrays
Abstract / Description: 

Recently cold atoms in optical tweezer arrays have emerged as a versatile platform for quantum science experiments. I will review some of these developments, specifically, atom-by-atom assembly [1] as a fast and simple method to generate defect-free atomic arrays and Rydberg-based quantum simulation of spin models. While already reaching competitive results, these systems are still in their infancy and limitations in coherence, detection fidelity, and scalability remain. I will outline how we can improve on these issues and open new avenues in quantum metrology by using alkaline earth atoms, followed by an overview of recent results: 1) A record in imaging-fidelity for neutral atoms and demonstration of narrow-line cooling in tweezers [2,3]. 2) High-fidelity Rydberg excitation from a clock state, including a record in entanglement-fidelity for two neutral atoms [4]. 3) Demonstration of an optical clock with single-atom detection in tweezer arrays [5].

 

[1] Endres et al., Science 354, 1024 (2016)

[2] Covey et. al, Phys. Rev. Lett. 122, 173201 (2019)

[3] Cooper et al., Phys. Rev. X 8, 041055 (2018)

[4] Madjarov*, Covey*, et al., arXiv:2001.04455 (2020)

[5] Madjarov et al., Phys. Rev. X 9, 041052 (2019)


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, February 11, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Quantum Physics from a computational complexity angle"

Topic: 
Quantum Physics from a computational complexity angle
Abstract / Description: 

Quantum computation is just around the corner, maybe; or it may take a few decades to see the true technological revolution it offers. Who knows. 

In any case, the field had already reshaped the way we think of quantum physics. Computational complexity notions such as quantum NP and interactive proofs shed light on old physics questions such as relaxation times and the nature of entanglement in ground states; as well as on how we understand what a quantum measurement really is. I will provide some examples of recent lines of research in quantum computation, which demonstrate how this blending of the computational complexity language into the heart of quantum physics can lead to some interesting new insights and questions. 


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, February 4, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Twisty fun in 2D materials"

Topic: 
Twisty fun in 2D materials
Abstract / Description: 

A van der Waals bonded solid consists of sheets of two-dimensional (2D) atomic layers with strong bonding in-plane. When these crystals are grown naturally, the stacking order along the out-of-plane dimension is dictated by the van der Waals force, typically leading to all layers of the crystal being oriented in the same in-plane direction. Recently, it has become possible to synthetically create materials where the individual layers have arbitrary in-plane direction relative to each other. These materials are of great interest theoretically since they realize new crystal structures not achievable in nature, with new emergent properties predicted. One of the key experimental findings in one such material last year was the presence of superconductivity and Mott insulating behavior in twisted bilayer graphene, properties that the individual layers do not display by themselves. In this talk, I will describe STM and transport properties of three such materials: (a) twisted bilayer graphene, where we measure the electronic structure of the material that is a Mott insulator (b) twisted bilayer WSe2, where we also observe Mott insulating behavior and (c) twisted double bilayer graphene, where we have evidence from STM for excitonic insulator behavior as well as the presence of chiral topological edge states in the interior of the material.


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, January 28, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Space Observatories of the Highest Energy Particles: POEMMA & EUSO-SPB"

Topic: 
Space Observatories of the Highest Energy Particles: POEMMA & EUSO-SPB
Abstract / Description: 

What are the mysterious sources of the most energetic particles ever observed? What are the sources of energetic cosmic neutrinos? How do particles interact at extreme energies?


Building on the progress achieved by the ground-based Auger Observatory in studying cosmic particles that reach 100 EeV, an international collaboration is working on space and sub-orbital missions to answer these questions. The Extreme Universe Space Observatory (EUSO) on a super pressure balloon (SPB) is designed to detect ultra-high energy cosmic rays (UHECRs) from above. EUSO-SPB1 flew in 2017 with a fluorescence telescope. EUSO-SPB2 is being built to observe both fluorescence and Cherenkov from UHECRs and neutrinos. These sub-orbital missions lead to POEMMA, the Probe Of Extreme Multi-Messenger Astrophysics, a space mission designed to discover the sources of UHECRs and to observe neutrinos above 20 PeV from energetic transient events. POEMMA will open new Multi-Messenger windows onto the most energetic events in the Universe, enabling the study of new astrophysics and particle physics at these otherwise inaccessible energies


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, January 21, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Quantum oscillations in solids: past, present and future"

Topic: 
Quantum oscillations in solids: past, present and future
Abstract / Description: 

On a visit to Stanford to honor Ted Geballe's centennial, I think it is appropriate to talk about an aspect of condensed matter and materials physics that has spanned his entire professional lifetime. The de Haas – van Alphen effect is one of the most profound and pronounced manifestations of quantum mechanics in solids. Discovered in Leiden fully ninety years ago as a signal in the magnetic torque of bismuth, the effect is now observed in a huge range of physical properties, and often given the general name of 'quantum oscillations'. The quest from discovery to full understanding required seminal contributions from some of the most celebrated names of twentieth century physics, such as Landau, Onsager and Lifshitz. The true hero of the technique, perhaps less well known than the above friends and colleagues with whom he collaborated, was the Cambridge-based Russian experimental physicist David Shoenberg. I had the privilege of knowing David for the last ten years of his life, and of learning about quantum oscillations from him and from his protégé Gil Lonzarich. In this talk I will review the historical development of the field, and try to show how important it has been, as a driver for the development of low temperature-low noise experimental techniques, for the growth of high purity single crystals, and for the introduction of key concepts in the theory of solids. I will close by stressing that the party is far from over. New physics associated with the de Haas – van Alphen effect still at the forefront of condensed matter science to this day, and there is an ongoing search for even more exotic relatives that are predicted to exist in certain special many-body systems.


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, January 14, 2020 - 4:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium presents "Quantum Sensing of Quantum Materials"

Topic: 
Quantum Sensing of Quantum Materials
Abstract / Description: 

The magnetic fields generated by spins and currents provide a unique window into the physics of correlated-electron materials and devices. Proposed only a decade ago, magnetometry based on the electron spin of nitrogen-vacancy (NV) defects in diamond is emerging as a platform that is exceptionally suited for probing condensed matter systems: it can be operated from cryogenic temperatures to above room temperature, has a dynamic range spanning from DC to GHz, and allows sensor-sample distances as small as a few nanometers. As such, NV magnetometry provides access to static and dynamic magnetic and electronic phenomena with nanoscale spatial resolution. While pioneering work focused on proof-of-principle demonstrations of its nanoscale imaging resolution and magnetic field sensitivity, now experiments are starting to probe the correlated-electron physics of magnets and superconductors and to explore the current distributions in low-dimensional materials. In this talk, I will review some of our recent work that uses NV center magnetometry to image skyrmions in thin magnetic films, measure the spin chemical potential in magnetic insulators, and image hydrodynamic electron flow in graphene.

 


Winter Qtr. Colloq. committee: M. Schleier-Smith (Chair), B. Cabrera, S. Dimopoulos, T. Heinz, S. Kachru & L. Tompkins
Location: Hewlett Teaching Center, Rm. 200

Date and Time: 
Tuesday, January 7, 2020 - 4:30pm
Venue: 
Hewlett 200

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