Metrology seminars

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.

Quantum information methods can improve the design of precision sensors. This talk first uses error correction to distinguish suppressible noise from disturbances inseparable from the signal, extending from individual qubits to collective and distributed sensing. It then applies ideas from tomography, certification and purification to estimating several parameters at once. The proposed measurement protocols address incompatible observables while seeking practical implementation and near-optimal sensitivity.

Sisi Zhou derives instance-optimal sample-complexity bounds for high-precision shadow tomography using measurements on one or a few copies at a time. For a given observable set, an optimisation formula involving the inverse Fisher-information matrix characterises the necessary and sufficient number of copies up to a logarithmic factor. The result links quantum learning and quantum metrology and includes adaptive measurements and potentially dimension-dependent precision thresholds.

Jun Ye discusses how laser science and increasingly large coherent quantum systems are expanding precision measurement into nuclear physics. Experiments now maintain coherence in thousands of atoms for minutes and resolve quantum states of the thorium-229 nuclear transition. A vacuum-ultraviolet frequency comb enables coherent excitation of that transition and connects its frequency directly to a highly precise atomic clock. The lecture examines how this connection between atomic and nuclear measurement could support new tests of fundamental physics and nuclear clocks containing billions of absorbers, with the prospect of surpassing the timekeeping capabilities of existing atomic clocks.

Olivier Guyon explains the physics and engineering of extreme adaptive optics for directly imaging exoplanets. Atmospheric turbulence distorts incoming wavefronts; sensors measure those distortions and deformable mirrors apply compensating corrections. The lecture covers guide stars, fast detectors, actuators, real-time computing and control systems. Extreme adaptive optics requires correction rates above a kilohertz, mirrors with more than a thousand actuators and nanometer-scale measurements of optical aberrations. Guyon describes how integrated systems suppress and calibrate unwanted starlight, including approaches developed with the Subaru Extreme Adaptive Optics system. These advances support efforts to equip extremely large telescopes to image potentially habitable planets.