arXiv subjects
Publications and source records attributed to T. Tyc.
We show that a pulse of electromagnetic radiation launched into a cavity can be completely absorbed into an infinitesimal region of space, provided one has a high degree of control over the current flowing through this region. We work out explicit examples of this effect in a cubic cavity and a cylindrical one, and experimentally demonstrate the effect in the microwave regime.
In this work we investigate an influence of decoherence effects on quantum states generated as a result of the cross-Kerr nonlinear interaction between two modes. For Markovian losses (both photon loss and dephasing), a region of parameters when losses still do not lead to destruction of non-classicality is identified. We emphasize the difference in impact of losses in the process of state generation as opposed to those occurring in propagation channel. We show moreover, that correlated losses in modern realizations of schemes of large cross-Kerr nonlinearity might lead to enhancement of non-classicality.
The quantum marginal problem asks what local spectra are consistent with a given spectrum of a joint state of a composite quantum system. This setting, also referred to as the question of the compatibility of local spectra, has several applications in quantum information theory. Here, we introduce the analogue of this statement for Gaussian states for any number of modes, and solve it in generality, for pure and mixed states, both concerning necessary and sufficient conditions. Formally, our result can be viewed as an analogue of the Sing-Thompson Theorem (respectively Horn's Lemma), characterizing the relationship between main diagonal elements and singular values of a complex matrix: We find necessary and sufficient conditions for vectors (d1, ..., dn) and (c1, ..., cn) to be the symplectic eigenvalues and symplectic main diagonal elements of a strictly positive real matrix, respectively. More physically speaking, this result determines what local temperatures or entropies are consistent with a pure or mixed Gaussian state of several modes. We find that this result implies a solution to the problem of sharing of entanglement in pure Gaussian states and allows for estimating the global entropy of non-Gaussian states based on local measurements. Implications to the actual preparation of multi-mode continuous-variable entangled states are discussed. We compare the findings with the marginal problem for qubits, the solution of which for pure states has a strikingly similar and in fact simple form.
We present two experimental schemes to perform continuous variable (2,3) threshold quantum secret sharing on the quadratures amplitudes of bright light beams. Both schemes require a pair of entangled light beams. The first scheme utilizes two phase sensitive optical amplifiers, whilst the second uses an electro-optic feedforward loop for the reconstruction of the secret. We examine the efficacy of quantum secret sharing in terms of fidelity, as well as the signal transfer coefficients and the conditional variances of the reconstructed output state. We show that both schemes in the ideal case yield perfect secret reconstruction.
The k-electron correlation function of a free chaotic electron beam is derived with the spin degree of freedom taken into account. It is shown that it can be expressed with the help of correlation functions for a polarized electron beam of all orders up to k and the degree of spin polarization. The form of the correlation function suggests that if the electron beam is not highly polarized, observing multi-particle correlations should be difficult. The result can be applied also to chaotic photon beams, the degree of spin polarization being replaced by the degree of polarization.
I show that there exists a class of inequalities between correlation functions of different orders of a chaotic electron field. These inequalities lead to the antibunching effect and are a consequence of the fact that electrons are fermions -- indistinguishable particles with antisymmetric states. The derivation of the inequalities is based on the known form of the correlation functions for the chaotic state and on the properties of matrices and determinants.