October 2019
Abstracts of the QSIT Lunch Seminar, Thursday, October 3, 2019
Efficient two-qubit gate calibration using Bayesian estimation
Brennan de Neeve - Trapped Ion Quantum Information Group (Home group), ETH Zurich
Quantum computing experiments face the challenge of scaling to higher complexity while significantly increasing fidelities. In this context, fast calibration of experimental settings becomes an essential tool. In my talk I will describe recent results on the calibration of two-qubit gates performed on a trapped-ion quantum processor, using an approach which considers the calibration problem as a quantum metrology problem and uses Bayes' rule to learn desired parameters. An attractive feature of these methods is that the parameter estimation is updated following each experimental measurement of the two ions using an embedded control system. First experiments demonstrate the efficiency of this approach as compared to previous techniques. An outlook will be given towards extensions of the methods to larger systems.
Motional Sideband Asymmetry of a Nanoparticle Optically Levitated in Free Space
Felix Tebbenjohanns - Photonics Laboratory (Novotny group), ETH Zurich
A well-known quantum effect from Raman spectroscopy is the asymmetry between Stokes and anti-Stokes scattering which can be used to probe the local temperature of a sample [1]. It can be understood as a consequence of the existence of the ground-state of the molecular vibration, since from there the vibration cannot emit energy to the light field. In cavity optomechanics, Raman-sideband spectroscopy is used to measure the motional energy of a mechanical oscillator [2-4].
We optically levitate a 136 nm sized particle in free-space and observe its motion in the trap. Under feedback-cooling, we observe the Raman-sideband asymmetry arising from the existence of the quantum ground state of the particle’s center-of-mass motion [5]. Our system is the first to allow for sideband thermometry in optomechanics without the need to couple the mechanical oscillator to an optical cavity.
References:
[1] B. J. Kip and R. J. Meier, Applied Spectroscopy44, 707 (1990)
[2] A. H. Safavi-Naeini, J. Chan, J. T. Hill, T. P. M. Alegre, A. Krause, and O. Painter, Phys. Rev. Lett.108, 033602 (2012)
[3] A. J. Weinstein, C. U. Lei, E. E. Wollman, J. Suh, A. Metelmann, A. A. Clerk, and K. C. Schwab, Phys. Rev. X4, 041003 (2014)
[4] T. P. Purdy, P.-L. Yu, N. S. Kampel, R. W. Peterson, K. Cicak, R. W. Simmonds, and C. A. Regal, Phys. Rev. A92, 031802(R) (2015)
[5] F. Tebbenjohanns, M. Frimmer, V. Jain, D. Windey, and L. Novotny, arxiv:1908.05079 (2019)