Southwest Quantum Information and Technology
Fourteenth Annual Meeting, February 16-19, 2012
Albuquerque, New Mexico
Full Program | Thursday | Friday | Saturday | Sunday | All Sessions
| SESSION 1: Tomography - Alvarado "D" | Session Chair: |
| 4:00pm-4:30pm | Steven Flammia, University of Washington | Direct Fidelity Estimation from Few Pauli Measurements | Abstract. We describe a simple method for certifying that an experimental device prepares a desired quantum state rho. Our method is applicable to any pure state rho, and it provides an estimate of the fidelity between rho and the actual (arbitrary) state in the lab, up to a constant additive error. The method requires measuring only a constant number of Pauli expectation values, selected at random according to an importance-weighting rule. Our method is faster than full tomography by a factor of d, the dimension of the state space, and extends easily and naturally to quantum channels. This is joint work with Yi-Kai Liu. |
| 4:30pm-5:00pm | Brian Anderson, University of Arizona | Quantum Control and Quantum State Tomography in the Hyperfine Ground Manifold of Atomic Cesium | Abstract. Aaron Smith, Brian E. Anderson, Hector Sosa Martinez, Poul Jessen Center for Quantum Information and Control (CQuIC), College of Optical Science and Department of Physics, University of Arizona Carlos Riofrio, Ivan H. Deutsch Center for Quantum Information and Control (CQuIC), Department of Physics and Astronomy, University of New Mexico Quantum systems with Hilbert space dimension greater than two (qudits) provide an alternative to qubits as carriers of quantum information, and may prove advantageous for quantum information tasks if good laboratory tools for qudit manipulation and readout can be developed. We have successfully implemented a protocol for arbitrary quantum state-to-state mapping in the 16 dimensional hyperfine ground manifold of Cesium 133 atoms, using only static, radio frequency (rf) and microwave magnetic fields to drive the atomic evolution. This system is controllable given rf and microwave fields with constant amplitude and frequency, and piecewise constant phase modulation. Control waveforms (rf and microwave phases versus time) are found by numerical optimization, and can be designed to work well in the presence of errors in the driving and background magnetic fields. Experimentally, we achieve an average state mapping fidelity of 99% for a sample of randomly chosen target states. To perform quantum state tomography, we drive an ensemble of identically prepared atoms with phase modulated rf and microwave magnetic fields, and simultaneously probe them by coupling an atomic spin observable to the polarization of a near-resonant optical probe field. A measurement of the probe polarization then yields an informationally complete measurement record that can be inverted to obtain an estimate of the unknown quantum state. We have reconstructed the full density matrix for a set of randomly chosen test states, using computer algorithms based either on least squares fitting or compressed sensing. The latter approach reconstructs our test states with an average fidelity above 90%, limited primarily by errors in applied drive fields. |
| 5:00pm-5:30pm | Steven van Enk, University of Oregon | Information criteria for quantum state estimation and everything else | Abstract. The thesis of this talk is that every good experiment (in which the experimentalist knows more or less what she is doing) can be analyzed efficiently, by using so-called information criteria developed for model selection. This holds true even for tomographically complete measurements on many-qubit systems. |