Fall 2021

Abstract: Understanding whether dissipation in an open quantum system is truly quantum is a question of both fundamental and practical interest. We consider a general model of n qubits subject to correlated Markovian dephasing, and present a sufficient condition for when bath-induced dissipation can generate system entanglement and hence must be considered quantum. Surprisingly, we find that the presence or absence of time-reversal symmetry (TRS) plays a crucial role: broken TRS is required for dissipative entanglement generation.

Abstract: Near-term applications of early quantum devices, such as quantum simulations, rely on accurate estimates of expectation values to become relevant. Decoherence and gate errors lead to wrong estimates. This problem was, at least in theory, remedied with the advent of quantum error correction.

Abstract: Studying the effect of local projective measurements on the scaling of entanglement entropy is an intense topic of research in the context of measurement-induced phase transitions. While it is traditionally studied in discrete circuit models, a close continuous-time analogy can be drawn with monitored open quantum dynamics, where a record of the registered quantum-jump clicks allows one to reconstruct the pure-state stochastic trajectories.

Abstract: In this special Friday Quantum Seminar, Dr. Allyson O'Brien, a Quantum Technology Scientist at Leidos, will share stories from her career path and a broader perspective on the field.
https://umd.zoom.us/j/99484119207
Pizza and drinks served after the talk.

Abstract: The paradigm of reservoir computing exploits the nonlinear dynamics of a physical reservoir to perform complex time-series processing tasks such as speech recognition and forecasting. Unlike other machine-learning approaches, reservoir computing relaxes the need for optimization of intra-network parameters, and is thus particularly attractive for near-term hardware-efficient quantum implementations.

Abstract: Theoretical models of quantum computation usually assume that 2-qubit gates can be performed between arbitrary pairs of qubits.

Abstract: What does it mean to simulate a quantum field theory? This is a challenging question because a majority of the quantum field theories relevant to fundamental physics lack a fully rigourous mathematical definition. Thus it is impossible in general to compare the predictions of discretised theories with their continuum counterparts. I will discuss these challenges and advocate the use of the recently introduced operator algebraic renormalization (OAR) as a means to provide both classical and quantum simulations of quantum field theories, in particular, conformal theories.

Abstract: Quantum process tomography is a critical capability for building quantum computers, enabling quantum networks, and understanding quantum sensors. Like quantum state tomography, the process tomography of an arbitrary quantum channel requires a number of measurements that scale exponentially in the number of quantum bits affected. However, the recent field of shadow tomography, applied to quantum states, has demonstrated the ability to extract key information about a state with only polynomially many measurements.

Abstract: New experimental methods such as nitrogen vacancy center magnetometry allow for the imaging of local transport phenomena well below the micron length scale. I will describe how these methods might be used to experimentally reveal quantum critical dynamics which is invisible in conventional bulk transport measurements. Using a holographic system as a toy model, I will describe what happens as current is pushed through a geometric constriction in both hydrodynamic and quantum critical transport regimes, both in charge neutral and non-zero density limits.