Quantum Science Seminar #56 - Hot Topics #04

Paula Garcia Molina
IFF-CSIC
Madrid — Spain
Variational quantum algorithm for eigenvalue problems of a class of Schrödinger-type partial differential equations
We develop a variational quantum algorithm to solve partial differential equations (PDE's) using a space-efficient variational ansatz that merges structured quantum circuits for coarse-graining with Fourier-based interpolation. Variational circuits represent symmetrical smooth functions as the ansatz, and we combine them with different classical optimizers that differ on the gradient calculation: no gradient, numerical gradient and analytic gradient. As benchmark, we show the results for the computation of the ground state of the one-dimensional quantum harmonic oscillator. In idealized quantum computers, the infidelity is of order 10^{−5} with 3 qubits, and these fidelities can be approached in real noisy quantum computers, either directly or through error mitigation techniques. However, we find that the precision is sub-par with other classical methods, suggesting the need for better strategies in the optimization and the evaluation of the cost function itself.
Gadi Afek
Yale University
New Haven — Connecticut — U.S.A.
Precision searches for new physics using optically levitated sensors
In an attempt to provide further insight into one of the major questions of physics beyond the standard model, highly sensitive optomechanical sensors are developed utilizing techniques from the field of atomic physics. These sensors are table-top experimental tools offering exquisite control of mechanical, rotational and electrical degrees of freedom of an optically levitated ~ng mass in vacuum, enabling unprecedented acceleration and force sensitivities for these mass scales. I will present two recent searches, the first looking for recoils from passing DM particles and the second for deviations from charge neutrality and so-called "millicharged particles". For certain, well-motivated dark matter models, these searches exceed the sensitivity of even large-scale experiments, thereby offering a complementary approach.
Chi Shu
MIT
Cambridge — Massachussetts — U.S.A
Quantum-Enhanced Optical Lattice Clock
Optical atomic clocks which are primarily limited by the quantum projection noise can reach stability of 10^{-19} in about one hour. By Hamiltonian engineering, optical clocks with quantum entangled states can reach better stability in a shorter time, thus opening the possibility to survey physics at higher frequency range. I will report the progress of our effort on quantum-enhanced optical lattice clocks. With cavity feedback squeezing and coherent optical state transfer, we demonstrate entanglement on optical clock transition in Yb-171. We achieve a metrological improvement of 4.4 dB over the standard quantum limit (SQL). Recently, we performed a signal amplification through time-reversed interaction (SATIN) protocol achieving the largest sensitivity improvement beyond SQL in any interferometer to date at 11.8(5) dB between the ground state magnetic sublevels. Together with the future effort in improving the local oscillator laser stability, we are one step closer to the fully operational quantum-enhanced optical atomic clock.

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