Cavity-enabled high-dimensional quantum key distribution

High-dimensional quantum key distribution (QKD) offers the possibility of encoding multiple bits of key on a single entangled photon pair. An experimentally promising approach to realizing this is to use energy–time entanglement. Currently, however, the control of very high-dimensional entangled photons is challenging. We present a simple and experimentally compact approach, which is based on a cavity that allows one to measure two different bases: the time of arrival and another that is approximately mutually unbiased to the arrival time. We quantify the errors in the setup, due both to the approximate nature of the mutually unbiased measurement and as a result of experimental errors. It is shown that the protocol can be adapted using a cut-off so that it is robust against the considered errors, even within the regime of up to 10 bits per photon pair

Maximum observable correlation for a bipartite quantum system

The maximum observable correlation between the two components of a bipartite quantum system is a property of the joint density operator, and is achieved by making particular measurements on the respective components. For pure states it corresponds to making measurements diagonal in a corresponding Schmidt basis. More generally, it is shown that the maximum correlation may be characterised in terms of a `correlation basis' for the joint density operator, which defines the corresponding (nondegenerate) optimal measurements. The maximum coincidence rate for spin measurements on two-qubit systems is determined to be (1+s)/2, where s is the spectral norm of the spin correlation matrix, and upper bounds are obtained for n-valued measurements on general bipartite systems. It is shown that the maximum coincidence rate is never greater than the computable cross norm measure of entanglement, and a much tighter upper bound is conjectured. Connections with optimal state discrimination and entanglement bounds are briefly discussed.Comment: Revtex, no figure

The information of high-dimensional time-bin encoded photons

We determine the shared information that can be extracted from time-bin entangled photons using frame encoding. We consider photons generated by a general down-conversion source and also model losses, dark counts and the effects of multiple photons within each frame. Furthermore, we describe a procedure for including other imperfections such as after-pulsing, detector dead-times and jitter. The results are illustrated by deriving analytic expressions for the maximum information that can be extracted from high-dimensional time-bin entangled photons generated by a spontaneous parametric down conversion. A key finding is that under realistic conditions and using standard SPAD detectors one can still choose frame size so as to extract over 10 bits per photon. These results are thus useful for experiments on high-dimensional quantum-key distribution system.Comment: 18 pages, 6 figure

Income and transfer tax integration: Historic policy links for wealth transfer tax restructuring

The proposals listed herein are an outgrowth of recent study by this author and Ms. Sharon K. Brougham, M.T., C.P. A., who is a doctoral accounting student at the University of Colorado at Boulder. The scope of this article does not allow for full elaboration so only key highlights of the study are listed. The overall intent is to update prior discussions on estate-income tax unification and to foster further debate as to the efficacy of retaining the present dual-track system of taxation on individuals. It is not, however, intended to be the finite blueprint of tax reform. The full study is scheduled to be published in the Akron Tax Law Journal along with the A.B.A. Report

Security of high-dimensional quantum key distribution protocols using Franson interferometers

Franson interferometers are increasingly being proposed as a means of securing high-dimensional energy-time entanglement-based quantum key distribution (QKD) systems. Heuristic arguments have been proposed that purport to demonstrate the security of these schemes. We show, however, that such systems are vulnerable to attacks that localize the photons to several temporally separate locations. This demonstrates that a single pair of Franson interferometers is not a practical approach to securing high-dimensional energy-time entanglement based QKD. This observations leads us to investigate the security of modified Franson-based-protocols, where Alice and Bob have two or more Franson interferometers. We show that such setups can improve the sensitivity against attacks that localize the photons to multiple temporal locations. While our results do not constituting a full security proof, they do show that a single pair of Franson interferometers is not secure and that multiple such interferometers could be a promising candidate for experimentally realizable high-dimensional QKD.Comment: 14 pages (single column format

A Proposal for Restructuring the Taxation of Wealth Transfers: Tax Reform Redux?

The Tax Reform Act of 1986 (TRA\u2786) provided for the most dramatic changes to the Internal Revenue Code since its inception over seventy years ago. The stated purposes of these reforms were to promote fairness, simplicity, and economic growth. The short-term success of these measures has yet to be ascertained. It is the position of this article that the long-term prospects for ultimate individual tax reform cannot be divorced from an eventual restructuring of the present federal wealth transfer taxation system, currently consisting of the estate, gift, and generation-skipping taxes. Genuine tax reform will remain unfinished business until such time as these transfers are fully interwoven into a reconstituted individual taxation system. It is time for an integrated system which interpolates the best elements of the newly passed income tax reforms while at the same time jettisoning the cumbersome, complicated and inefficient elements of the present wealth transfer taxes. This proposal is offered in the hope of changing the direction of future research and discussion away from the patchwork repairs of the past towards a new integrated system of taxation

Interference of composite bosons

We investigate multi-boson interference. A Hamiltonian is presented that treats pairs of bosons as a single composite boson. This Hamiltonian allows two pairs of bosons to interact as if they were two single composite bosons. We show that this leads to the composite bosons exhibiting novel interference effects such as Hong-Ou-Mandel interference. We then investigate generalizations of the formalism to the case of interference between two general composite bosons. Finally, we show how one can realize interference between composite bosons in the two atom Dicke model

Cloning and Joint Measurements of Incompatible Components of Spin

A joint measurement of two observables is a {\it simultaneous} measurement of both quantities upon the {\it same} quantum system. When two quantum-mechanical observables do not commute, then a joint measurement of these observables cannot be accomplished by projective measurements alone. In this paper we shall discuss the use of quantum cloning to perform a joint measurement of two components of spin associated with a qubit system. We introduce a cloning scheme which is optimal with respect to this task. This cloning scheme may be thought to work by cloning two components of spin onto its outputs. We compare the proposed cloning machine to existing cloners.Comment: 7 pages, 2 figures, submitted to PR

Transformation design and nonlinear Hamiltonians

We study a class of nonlinear Hamiltonians, with applications in quantum optics. The interaction terms of these Hamiltonians are generated by taking a linear combination of powers of a simple `beam splitter' Hamiltonian. The entanglement properties of the eigenstates are studied. Finally, we show how to use this class of Hamiltonians to perform special tasks such as conditional state swapping, which can be used to generate optical cat states and to sort photons.Comment: Accepted for publication in Journal of Modern Optic