arXiv subjects

C. R. Stroud Jr

Publications and source records attributed to C. R. Stroud Jr.

7 recordsLinked to original sources

arXiv2018

Influence of Vacuum modes on Photodetection

Photodetection is a process in which an incident field induces a polarization current in the detector. The interaction of the field with this induced current excites an electron in the detector from a localized bound state to a state in which the electron freely propagates and can be classically amplified and detected. The induced current can interact not only with the applied field, but also with all of the initially unpopulated vacuum modes. This interaction with the vacuum modes is assumed to be small and is neglected in conventional photodetection theory. We show that this interaction contributes to the quantum efficiency of the detector. We also show that in the Purcell enhancement regime, shot noise in the photocurrent depends on the bandwidth of the the vacuum modes interacting with the detector. Our theory allows design of sensitive detectors to probe the properties of the vacuum modes.

quant-ph↗

arXiv2009

Steady-State Two Atom Entanglement in a Pumped Cavity Enhanced by Nonlinear Mirrors

We demonstrate the steady-state entanglement of two two-level atoms inside a pumped cavity with photon leakage through a nonlinear mirror and through spontaneous decay, and show that the entanglement is enhanced by the presence of a nonlinear mirror. Our model assumes the vacuum Rabi splitting of the dressed states of the system to be much larger than any of the decay parameters of the system. We also discuss how the dressed states of the system offer us intuition as to where the entanglement lies in the state space spanned by the system, and allow us the optimize the system.

quant-ph↗

arXiv2009

Steady-State Two Atom Entanglement in a Pumped Cavity

In this paper we explore the possibility of a steady-state entanglement of two two-level atoms inside a pumped cavity by taking into account cavity leakage and the spontaneous emission of photons by the atoms. We describe the system in the dressed state picture in which the coherence is built into the dressed states while transitions between the dressed states are incoherent. Our model assumes the vacuum Rabi splitting of the dressed states to be much larger than any of the decay parameters of the system which allows atom-field coherence to build up before any decay process takes over. We show that, under our model, a pumping field cannot entangle two closed two-level atoms inside the cavity in the steady-state, but a steady-state entanglement can be achieved with two open two-level atoms.

quant-ph↗

arXiv2004

Robust Multi-Partite Multi-Level Quantum Protocols

We present a tripartite three-level state that allows a secret sharing protocol among the three parties, or a quantum key distribution protocol between any two parties. The state used in this scheme contains entanglement even after one system is traced out. We show how to utilize this residual entanglement for quantum key distribution purposes, and propose a realization of the scheme using entanglement of orbital angular momentum states of photons.

quant-ph↗

arXiv2001

Quantum fast Fourier transform using multilevel atoms

We propose an implementation of the quantum fast Fourier transform algorithm in an entangled system of multilevel atoms. The Fourier transform occurs naturally in the unitary time evolution of energy eigenstates and is used to define an alternate wave-packet basis for quantum information in the atom. A change of basis from energy levels to wave packets amounts to a discrete quantum Fourier transform within each atom. The algorithm then reduces to a series of conditional phase transforms between two entangled atoms in mixed energy and wave-packet bases. We show how to implement such transforms using wave-packet control of the internal states of the ions in the linear ion-trap scheme for quantum computing.

quant-ph↗

arXiv2001

Entanglement of internal and external angular momenta of a single atom

We consider the exchange of spin and orbital angular momenta between a circularly polarized Laguerre-Gaussian beam of light and a single atom trapped in a two-dimensional harmonic potential. The radiation field is treated classically but the atomic center-of-mass motion is quantized. The spin and orbital angular momenta of the field are individually conserved upon absorption, and this results in the entanglement of the internal and external degrees of freedom of the atom. We suggest applications of this entanglement in quantum information processing.

quant-ph↗

arXiv2001

Atomic wave packet basis for quantum information

We propose a wave packet basis for storing and processing several qubits of quantum information in a single multilevel atom. Using radially localized wave packet states in the Rydberg atom, we construct an orthogonal basis that is related to the usual energy level basis by a quantum Fourier transform. A transform-limited laser pulse that is short compared with the classical Kepler period of the system interacts mainly with the wave packet state localized near the atomic core, allowing selective control in this basis. We argue that wave packet control in this regime is useful for multilevel quantum information processing.

quant-ph↗