Quantum Initiative: Quantum Lunch

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121.

The organizing committee includes Malcolm Boshier (P-21), Lukasz Cincio (T-4), Diego Dalvit (T-4), Changhyun Ryu (P-21) , Nikolai Sinitsyn (T-4), Rolando Somma (T-4), Yigit Subasi (T-4), Christopher Ticknor (T-1), and Wojciech Zurek (T-4).

For more information, or to nominate a speaker, contact Yigit Subasi or Lukasz Cincio.

To add your name to the Quantum Lunch email list, contact Amanda Martinez.

Thursday, November 1, 2018
12:30 PM - 2:00 PM

Speaker: Luis Pedro Garcia-Pintos (U. Mass, Boston)

Technical Host: Lukasz Cincio

TOPIC: Consequences of measurement back-action from quantum monitoring: non-standard speed limits and spontaneous symmetry breaking

Abstract
The information acquired during the monitoring of a quantum system provides a state description that can differ greatly from the description given by agents ignorant of the outcomes. While the lack of information in the later results in a mixed density matrix following open system dynamics, the measurement back-action in the former case provides a more accurate description. We study the consequences of such measurement back-action to two problems in quantum theory: the derivation of limits to the speed of evolution, and the process of spontaneous symmetry breaking. For the problem of the speed of evolution, we show that that there are trajectories for which standard quantum speed limits are violated, and we provide estimates for the range of velocities in an ensemble of realizations of continuous measurement records. We determine the dispersion of the speed of evolution and characterize the full statistics of single trajectories. Regarding the problem of spontaneous symmetry breaking, which is typically understood as a consequence of random fluctuations either in the Hamiltonian governing the evolution or in the state of the system, we present a novel alternative mechanism, induced by the measurement back-action. Unlike in the standard picture, our approach is dynamical and purely quantum mechanical in nature. We show that, depending on the nature of the quantum monitoring, an observer can thus alter the topology and the pattern of symmetry breaking.

Based on: “Quantum speed limits under continuous quantum measurements”, Luis Pedro Garcia-Pintos and Adolfo del Campo, arXiv:1804.01600; “Spontaneous symmetry breaking induced by quantum monitoring”, Luis Pedro Garc ´ia-Pintos, Diego Tielas, and Adolfo del Campo, arXiv:1808.08343.