Date:
Mon, 12/05/202512:00-13:30
Location:
Place: Levin building, Lecture Hall No. 8
Lecturer: Prof. Jonathan Ruhman, Bar Ilan
Abstract:
Measurement-induced phase transitions (MPT) are a class of dynamical phase transitions occurring in quantum many-body states undergoing non-unitary time evolution. For concreteness, consider a unitary evolution operator interspersed with local projective measurements. The transition is driven by p, the probability of a measurement appearing, both in space and time. As p is increased a sharp transition occurs between the "entangling" phase, where the system develops an extensive amount of entanglement, and the "dientagling" phase, where the measurements suppress entanglement and push the system to a steady state, very close to a product state. Such transitions can be important to quantum computation (e.g. to the applicability of quantum error correction codes in noisy quantum computers) and to the classical simulability of open quantum systems. In this talk I will provide an intuitive picture to understand the origin of this transition, by mapping quantum states evolving in time to a problem of percolation in d+1 dimensions [1,2,3]. I will explain why the percolation threshold provides only a bound on the true MPT, and show that in general, the two critical points differ. The universal properties of the MPT remain unknown and are the subject of ongoing research. I will conclude by presenting two recent approaches we have taken to attack this problem.
[1] D. Aharonov, "Quantum to Classical Phase Transition in Noisy Quantum Computers," Phys. Rev. A 62, 062311 (2000)
[2] A. Nahum, J. Ruhman, S. Vijay, and J. Haah, "Quantum Entanglement Growth under Random Unitary Dynamics," Phys. Rev. X 7, 031016 (2017)
[3] B. Skinner, J. Ruhman, and A. Nahum, MeasurementInduced Phase Transitions in the Dynamics of Entanglement, Phys. Rev. X 9, 031009 (2019)
Abstract:
Measurement-induced phase transitions (MPT) are a class of dynamical phase transitions occurring in quantum many-body states undergoing non-unitary time evolution. For concreteness, consider a unitary evolution operator interspersed with local projective measurements. The transition is driven by p, the probability of a measurement appearing, both in space and time. As p is increased a sharp transition occurs between the "entangling" phase, where the system develops an extensive amount of entanglement, and the "dientagling" phase, where the measurements suppress entanglement and push the system to a steady state, very close to a product state. Such transitions can be important to quantum computation (e.g. to the applicability of quantum error correction codes in noisy quantum computers) and to the classical simulability of open quantum systems. In this talk I will provide an intuitive picture to understand the origin of this transition, by mapping quantum states evolving in time to a problem of percolation in d+1 dimensions [1,2,3]. I will explain why the percolation threshold provides only a bound on the true MPT, and show that in general, the two critical points differ. The universal properties of the MPT remain unknown and are the subject of ongoing research. I will conclude by presenting two recent approaches we have taken to attack this problem.
[1] D. Aharonov, "Quantum to Classical Phase Transition in Noisy Quantum Computers," Phys. Rev. A 62, 062311 (2000)
[2] A. Nahum, J. Ruhman, S. Vijay, and J. Haah, "Quantum Entanglement Growth under Random Unitary Dynamics," Phys. Rev. X 7, 031016 (2017)
[3] B. Skinner, J. Ruhman, and A. Nahum, MeasurementInduced Phase Transitions in the Dynamics of Entanglement, Phys. Rev. X 9, 031009 (2019)
