Ben Baragiola, University of New Mexico
Traveling wave packets of light prepared with a definite number of photons, known as multimode Fock states, are well-suited for the role of "flying qubits" to relay information in a quantum computing device. In both the optical and microwave domain, propagating single-photon fields are routinely produced and manipulated, with ongoing progress toward higher photon numbers. If quantum technology is to take advantage of such nonclassical field states, a theoretical understanding of their interaction with the fundamental quantum components - a multilevel atom in cavity QED or a transmon in circuit QED, for example - is critical. A description of this interaction is complicated by the fact that, in contrast to vacuum and coherent fields, multimode Fock states are endowed with temporal-mode entanglement that drives non-Markovian reduced-state dynamics. Previously, we developed a master equation description for an arbitrary quantum system interacting with propagating Fock states [1], which has been used to study the cross-Kerr effect for single-photon detection in the microwave domain [2,3]. We have recently extended the method to situations in which the output fields are subject to continuous measurement - photon counting, homodyne, and heterodyne detection [4]. I will discuss the resulting Fock-state stochastic master equations, which describe conditional dynamics that can be used to prepare states of interest [5] and for feedback control in a variety of physical settings.
[1] BQB, R. Cook. A Branczyk, and J. Combes, N-photon wave packets interacting with an arbitrary quantum system, PRA 86, 013811 (2012).
[2] B. Fan, A. Kockum, J. Combes, G. Johannson, I. Hoi, C. Wilson, P. Delsing, G. Milburn, and T. Stace, Breakdown of the cross-Kerr scheme for photon counting, PRL 110, 053601 (2013)
[3] S. Sathyamoorthy, L. Tornberg, A. Kockum, BQB, J. Combes, C. Wilson, T. Stace, and G. Johansson. Quantum nondemolition detection of a propagating microwave photon, PRL 112, 093601 (2014)
[4] BQB and J. Combes, Quantum trajectories for systems probed with multi-mode Fock states, in preparation.
[5] N. Roch, M. Schwartz, F. Motzoi, C. Macklin, R. Vijay, A. Eddins, A. Korotkov, K. Whaley, M. Sarovar, and I. Siddiqi. Observation of measurement-induced entanglement and quantum trajectories of remote superconducting qubits.
PRL 112, 170501 (2014)