Spring 2022

Dissertation Committee Chair: Prof. Vladimir Manucharyan
Committee: 
Prof. Steven Anlage
Prof. Victor Galitski
Prof. Alicia Kollar
Prof. Ichiro Takeuchi

The field of Quantum Information is of great excitement in both fundamental physics and industry. One promising platform for quantum computing is gate-defined quantum dots in semiconductors. The greatest limiting factor currently is that delicate quantum states can lose their quantum nature due to interactions with their environment. Other open challenges are to coherently control large-scale spin qubits and develop methods to entangle quantum bits that are separated by significant distances.

Abstract: In most common metals, the many-body physics of their electrons can be described in terms of additive, weakly interacting excitations called quasiparticles. However, several examples of metallic states of matter related to the “high” temperature superconductors and other strongly correlated materials exist, in which strong electron-electron interactions near putative quantum critical points or phases lead to very unconventional physics that cannot be described by quasiparticles, even as the electron liquid remains compressible.

Abstract: Recent work has predicted that quenched near-integrable systems can exhibit dynamics associated with thermal,quantum,or purely nonequilibrium phase transitions, depending on the initial state[1]. Using a trapped-ion quantum simulator with intrinsic long-range interactions, we investigate collective non-equilibrium properties of critical fluctuations after quantum quenches.

Abstract: Quantum computers hold the promise of solving computational problems which are intractable using conventional methods. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit we encode quantum information in a distance-three logical qubit building up on recent distance-two error detection experiments [1].

Abstract: In the past decade, quantum simulators have increased in their power and scope, offering exquisite dynamical control of tens or even hundreds of individual atoms. Concurrently, a topological revolution in our understanding of electronic band structures has taken place, driven by the discovery of topological insulators, graphene and other topological materials. Remarkably, these advances can be connected --- the dynamics of driven few level systems can be described using band structures in "synthetic dimensions," one per driving tone.

Abstract: Over the last several decades, entanglement has emerged as a unifying lens for understanding phenomena across many areas in quantum physics. At low energy, the structure of ground state entanglement reflects universal features of the phase of matter. At high energy, the growth of entanglement underlies thermalization and the emergence of statistical mechanics. In this talk, I will describe two recent exact results characterizing entanglement in many-body systems.

Abstract: For quantum computers to achieve their promise, regardless of the qubit technology, significant improvements to both performance and scale are required.  Quantum-dot-based qubits in silicon have recently enjoyed dramatic advances in fabrication and control techniques.  The “exchange-only” modality is of particular interest, as it avoids control elements that are difficult to scale such as microwave fields, photonics, or ferromagnetic gradients.  In this control scheme, the entirety of quantum computation may be performed using only asynchronous, baseband voltage pulses on straig

Abstract: Quantum memory will play an important role in quantum networks, notably as components in quantum repeaters. One promising technique for realizing broadband quantum memory, the atomic frequency comb (AFC) protocol, calls for a material with large inhomogeneous broadening and small homogeneous broadening: spectral-hole burning techniques can be used to prepare the absorption spectrum in a periodic pattern of narrow peaks (an AFC). A single photon, absorbed as a collective excitation, will be re-emitted after a time interval fixed by the AFC tooth spacing.

Abstract: Quantum complexity is a measure of the minimal number of elementary operations required to approximately prepare a given state or unitary channel. Recently this concept has found applications beyond quantum computing---in the classification of topological phases of matter and in the description of chaotic many-body systems. Furthermore, within the context of the AdS/CFT correspondence, it has been postulated that the complexity of a specific time-evolved many-body quantum state is sensitive to the long-time properties of AdS-black hole interiors.