Quantum Physics

This Perimeter Institute conference brings together researchers studying quantum reference frames, quantum gravity, quantum foundations and related experiments. Topics include relational observables, quantum information in dynamical spacetime, locality, causality, entanglement, and the operational meaning of observers and subsystems. The meeting runs from 26 to 30 October 2026 in Waterloo, Canada. Registration is currently open, and the organizer provides information for virtual participation.

Sisi Zhou examines how quantum information methods can improve the precision of physical measurements. Qubit examples distinguish noise that quantum error correction can suppress from noise indistinguishable from the signal. The discussion extends to several qubits, phase estimation, many-body measurements and distributed sensors. A second part applies quantum-learning tools, including tomography, certification and purification, to estimation of several parameters. Because incompatible observables prevent all parameters from being measured optimally together, designing measurements is difficult. The talk presents practical protocols for several such sensing tasks that combine efficient implementation with sensitivity close to the optimum.

Theoretical physicist Jonathan Halliwell joins Steven Strogatz and Janna Levin to discuss how quantum decoherence helps explain the transition from wave-like quantum systems to the classical macroscopic world. The conversation covers quantum cosmology, decoherent histories, the measurement problem, macroscopic realism and why the quantum-to-classical transition does not require a conscious observer.

Carolina Paiva develops exact matrix product states for strongly interacting electrons in lattice bands. Conformal-field-theory correlation functions already provide exact representations of fractional quantum Hall trial wavefunctions, including Laughlin states. Extending the construction to fractional Chern insulators is obstructed by the lattice length scale. The talk shows how ideal Chern bands overcome that obstruction and derives an exact representation of Laughlin model states in a hybrid Wannier basis on a torus.

John Clarke, Michel H. Devoret and John M. Martinis trace the discovery that a macroscopic electrical circuit can display quantum tunnelling and discrete energy levels. Clarke connects early superconducting measuring devices with experiments on current-biased Josephson junctions. Microwave-induced resonances and the crossover from thermal activation to temperature-independent escape provide tests of quantum behaviour. Devoret explains how superconducting circuits became controllable artificial atoms, with Josephson elements enabling engineered energy spectra, qubits and quantum-limited amplifiers. He considers what these designed systems make possible beyond experiments with natural atoms. Martinis follows the development from early junction experiments to superconducting quantum processors. He discusses energy-level quantization, tunnelling, photon generation, quantum computational experiments, and the fabrication and error-control challenges involved in building useful machines.

Two postdoctoral researchers will study semiconductor quantum devices in the Quantum Functional System Research Group, led by Seigo Tarucha at the RIKEN Center for Emergent Matter Science. The work concerns silicon qubit characterization, multi-qubit systems, high-fidelity quantum operations and scalable quantum computing within Moonshot R&D Goal 6. Applicants need a doctorate in an experimental field such as semiconductor physics, quantum transport, electrical engineering or quantum information, or must obtain it before starting. The one-year appointment is renewable following evaluation, up to 31 March 2029.

Samuel Garratt presents rigorous upper limits on entanglement entropy for locally interacting quantum many-body states at fixed energy. Ground states usually exhibit an area law, unlike generic states whose entanglement scales with volume, and gapless systems can introduce corrections. The framework constrains ground-state entanglement for gapped and gapless systems in arbitrary spatial dimension, follows the transition toward volume-law behavior as energy increases, and bounds the computational resources needed to calculate response functions at zero temperature. These results connect spectral information with the cost of tensor-network calculations.