EE Student Information

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EE Student Information, Spring Quarter through Academic Year 2020-2021: FAQs and Updated EE Course List.

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QFarm

QFarm Quantum Seminar Series

Stanford Institute for Theoretical Physics presents "Replica wormhole and information retrieval in the SYK model coupled to Majorana chains"

Topic: 
Replica wormhole and information retrieval in the SYK model coupled to Majorana chains
Abstract / Description: 

Motivated by recent studies of the information paradox in (1+1)-D anti-de Sitter spacetime with a bath described by a (1+1)-D conformal field theory, we study the dynamics of second Rényi entropy of the Sachdev-Ye-Kitaev (SYK) model (χ) coupled to a Majorana chain bath (ψ). The system is prepared in the thermofield double (TFD) state and then evolved by HL+HR. For small system-bath coupling, we find that the second Rényi entropy S(2)χL,χR of the SYK model undergoes a first order transition during the evolution. In the sense of holographic duality, the long-time solution corresponds to a "replica wormhole". The transition time corresponds to the Page time of a black hole coupled to a thermal bath. We further study the information scrambling and retrieval by introducing a classical control bit, which controls whether or not we add a perturbation in the SYK system. The mutual information between the bath and the control bit shows a positive jump at the Page time, indicating that the entanglement wedge of the bath includes an island in the holographic bulk.

Date and Time: 
Monday, April 20, 2020 - 2:00pm
Venue: 
Zoom id: 165-492-015

Stanford Institute for Theoretical Physics presents "On the Entropy of an Einstein-Rosen Bridge"

Topic: 
On the Entropy of an Einstein-Rosen Bridge
Abstract / Description: 

We propose a new link between entropy and area: an eternal black hole with an ER bridge with cross-section A can carry quantum information, or be in a mixed state, with entropy S ≤ A/4GN . We provide evidence for our proposal in the context of AdS3 and JT gravity, by using the Island prescription and replica wormhole method for computing the Renyi entropy. We argue that a typical two sided black hole is described by a 'thermo-mixed double' state with only classical correlations between the two sides. Our reasoning suggests that an ER wormhole acts like a topological quantum memory, similar to the toric code.

Zoom id: 165-492-015 (Please note that this is a recurring id, valid till May 11.)

Date and Time: 
Monday, April 13, 2020 - 2:00pm
Venue: 
Zoom

QFarm Quantum Seminar Series presents "Generalized amplitude damping channel: The single greatest qubit mystery in quantum Shannon theory"

Topic: 
Generalized amplitude damping channel: The single greatest qubit mystery in quantum Shannon theory
Abstract / Description: 

The generalized amplitude damping channel (GADC) is one of the sources of noise in superconducting-circuit-based quantum computing. It can be viewed as the qubit analogue of the bosonic thermal channel, and it thus can be used to model lossy processes in the presence of background noise for low-temperature systems. In this work, we provide an information-theoretic study of the GADC. We first determine the parameter range for which the GADC is entanglement breaking and the range for which it is anti-degradable. We then establish several upper bounds on its classical, quantum, and private capacities. These bounds are based on data-processing inequalities and the uniform continuity of information-theoretic quantities, as well as other techniques. Our upper bounds on the quantum capacity of the GADC are tighter than the known upper bound reported recently in [Rosati et al., Nat. Commun. 9, 4339 (2018)] for the entire parameter range of the GADC, thus reducing the gap between the lower and upper bounds. We also establish upper bounds on the two-way assisted quantum and private capacities of the GADC. These bounds are based on the squashed entanglement, and they are established by constructing particular squashing channels. We compare these bounds with the max-Rains information bound, the mutual information bound, and another bound based on approximate covariance. For all capacities considered, we find that a large variety of techniques are useful in establishing bounds.

Joint work with Sumeet Khatri and Kunal Sharma

Date and Time: 
Wednesday, April 15, 2020 - 12:00pm
Venue: 
Zoom link: https://stanford.zoom.us/j/987676025

Stanford Institute for Theoretical Physics presents "Towards a 3d Ising model with a weakly-coupled string theory dual"

Topic: 
Towards a 3d Ising model with a weakly-coupled string theory dual
Abstract / Description: 

I'll discuss old and new motivations for a string theory description of the critical behavior of the 3d Ising model. Then I'll modify the Ising model so that the string theory is under better theoretical control, and describe the effects of this modification on the phase diagram. I'll conclude with some comments about the worldsheet theory.

Based on 2003.04349, with Nabil Iqbal.

Date and Time: 
Monday, April 6, 2020 - 2:00pm
Venue: 
Zoom id: 165-492-015

Q-Farm RELATED: SITP Seminar "Statistical mechanics of near extremal black holes"

Topic: 
Statistical mechanics of near extremal black holes
Abstract / Description: 

I will argue that 2D Jackiw-Teitelboim (JT) gravity is a good approximation for some observables related to near extremal black holes in higher dimensions, beyond the semiclassical limit. In the first part of the talk I will apply this to the calculation of the density of states of charged black holes in 4D and give a resolution of the thermodynamic "mass gap" puzzle. In the second part, I will apply this to the calculation of the partition function and IR limit of boundary correlators of near extremal rotating BTZ in 3D. An independent boundary 2D CFT bootstrap argument shows that the emergence of a JT gravity sector is universal.

Date and Time: 
Monday, March 30, 2020 - 2:00pm
Venue: 
Zoom id: 165-492-015

Q-FARM presents "Atom arrays of ultracold strontium: new tools for metrology and many-body physics"

Topic: 
Atom arrays of ultracold strontium: new tools for metrology and many-body physics
Abstract / Description: 

The development of microscopic detection of ensembles of neutral atoms has transformed our ability to study complex many-body systems. Techniques like quantum gas microscopy and optical tweezer arrays grant a unique single-particle-resolved perspective on solid-state analogs and idealized quantum spin models, as well as novel detection capabilities for quantities like entanglement. In this talk, I will describe our progress towards developing these tools for a new atomic species, strontium. In doing so, we establish new prospects enabled by the rich internal degrees-of-freedom associated with alkaline-earth atoms. I will report on our recent results in which we apply our platform to optical atomic clocks, a new application of optical tweezer arrays which indicates a number of strengths for metrology. In particular, I will describe our strategies for reaching arrays with hundreds of tweezers with sub-Hz atom-optical coherence, 41 seconds of atomic coherence, and atomic stability on par with the state-of-the-art. I will then describe our parallel progress towards engineering entanglement on an optical clock transition, as well as new scaling strategies involving atom-by-atom assembly in optical lattice potentials.

Date and Time: 
Wednesday, April 1, 2020 - 12:00pm
Venue: 
Zoom link: stanford.zoom.us/j/987676025

SITP Seminar presents "Conformal field theories with exceptional symmetry"

Topic: 
Conformal field theories with exceptional symmetry
Abstract / Description: 

In hopes of re-starting our seminar series, we will have our first virtual seminar via zoom on Monday, March 23 at 2pm. Before the seminar, we will begin with a virtual "town meeting" (again via zoom) from 1:30 to 2pm to just check with people on how everybody is doing during this uncertain period. Hope to see you there!

Zoom link: https://stanford.zoom.us/j/784962786


Despite being some of the first and most basic objects one encounters in the study of algebra, finite simple groups are surprisingly rich, and participate in a variety of mysterious connections to other areas in math and physics. The classification of finite simple groups is a remarkable theorem of pure mathematics which brings their mystique to bear. Indeed, much as in the more familiar classification of simple Lie groups, there are exceptional cases --- the so-called "sporadic groups" -- which are relatively poorly understood. Since group theory is the abstraction of the study of symmetry, it is natural to ask what structures exactly they act on by symmetries. Generalizing the observations of monstrous moonshine, we will argue that many of the sporadic groups naturally arise as the global symmetries of distinguished conformal field theories in two dimensions. In the process, we will be able to compute the torus partition functions of these theories by solving a kind of highly-constrained modular bootstrap problem using methods, old and new, from the theory of modular forms.

Date and Time: 
Monday, March 23, 2020 - 2:00pm
Venue: 
Zoom link: stanford.zoom.us/j/784962786

Q-Farm Quantum Seminar Series presents "Quantum Gravity in the Lab"

Topic: 
Quantum Gravity in the Lab
Abstract / Description: 
The trend of theoretical advances in AdS/CFT suggests that quantum gravity is broadly applicable as an effective description of chaotic many-body physics. Experimental realizations of such systems are now coming online, with more progress expected in the next few years. We can and should use tools of quantum gravity to describe the physics of these experiments. I will sketch one possible experiment exhibiting nontrivial behavior which, though perfectly understandable in hindsight using conventional methods, is motivated entirely by the physics of wormholes.

Live Broadcast and Recorded (no in-person meeting) - Zoom Link: https://stanford.zoom.us/j/987676025
Date and Time: 
Wednesday, March 18, 2020 - 12:00pm
Venue: 
Remote only

Q-Farm Quantum Seminar Series presents "Ultrafast Spectroscopy of Quantum Materials" and "Quantum and classical information spreading in many-body systems"

Topic: 
Ultrafast Spectroscopy of Quantum Materials and Quantum and classical information spreading in many-body systems
Abstract / Description: 

Ultrafast Spectroscopy of Quantum Materials: Quantum materials such as topological insulators, Weyl-semimetals, and atomically thin two-dimensional crystals have intriguing electronic properties, which makes them promising candidates for their potential applications in next-generation technology. Therefore, it is desirable to investigate the electronic properties of these materials through various methods such that their full potential, as well as the limitations, can be identified. In this talk, I will introduce a novel spectroscopic approach based on the use of strong ultrafast laser pulses and the generation of high-order harmonics. Analysis of temporal and spectral properties of high-order harmonics from these materials reveals their electronic band-structure, topology, as well as driven electron dynamics in the natural time scales of electrons. The advantages of this approach over conventional methods include the use of the all-optical setting, no physical contacts to samples, and much of the measurements that can be performed in ambient conditions. More importantly, the non-perturbative interactions between materials and strong laser fields could generate transient novel quantum phases, which can be subsequently probed by analyzing high-order harmonics.


 

Quantum and classical information spreading in many-body systems: I describe a new theoretical result that constrains how quantum information can spread through large systems. When a small subsystem interacts with a large environment, which information about the subsystem can we detect locally in the environment? In great generality, we show there exists at most an O(1)-sized region of the environment where quantum information about the subsystem can be locally detected, whereas in the rest of the environment, any locally detectible information about the subsystem must be classical information, and moreover this classical information can be modeled by measuring the subsystem in a fixed basis. We will discuss implications for many-body physics. This work builds on earlier work by Brandao et al. in arXiv:1310.8640.

Date and Time: 
Wednesday, March 4, 2020 - 12:00pm
Venue: 
Physics/Astrophysics (Varian II) Building, Room 102/103

Q-Farm Quantum Seminar Series presents "Long-lived interacting phases of matter protected by multiple time-translation symmetries in quasiperiodically driven systems"

Topic: 
Long-lived interacting phases of matter protected by multiple time-translation symmetries in quasiperiodically driven systems
Abstract / Description: 

The discrete time-translation symmetry of a periodically-driven (Floquet) system allows for the existence of novel, nonequilibrium interacting phases of matter. A well-known example is the discrete time crystal, a phase characterized by the spontaneous breaking of this time-translation symmetry. In this talk, I will show that the presence of *multiple* time-translational symmetries, realized by quasiperiodically driving a system with two or more incommensurate frequencies,  leads to a panoply of novel non-equilibrium phases of matter, both spontaneous symmetry breaking ("discrete time quasi-crystals") and topological.

In order to stabilize such phases, I will outline rigorous mathematical results establishing slow heating of systems driven quasiperiodically at high frequencies. As a byproduct, I will introduce the notion of many-body localization (MBL) in quasiperiodically driven systems. 

arXiv reference: 1910.03584

   

 

Date and Time: 
Wednesday, February 26, 2020 - 12:00pm
Venue: 
Physics/Astrophysics (Varian II) Building, Room 102/103

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