A simple effective model of charge ordered insulators is studied. The tight binding Hamiltonian c... more A simple effective model of charge ordered insulators is studied. The tight binding Hamiltonian consists of the effective on-site interaction U and the intersite density-density interactions Wij (both: nearest-neighbour and next-nearest-neighbour). In the analysis of the phase diagrams we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. The phase separated states have not been taken into account in previous analyses. Our investigations of two cases of the on-site interaction: attraction (U/(−WQ) = −10) and repulsion (U/(−WQ) = 1.1) show that, depending on the values of the next-nearest-neighbour attraction, the system can exhibit not only homogeneous phases: charge ordered (CO) and nonordered (NO), but also various phase separated states (CO-NO, CO-CO).
ABSTRACT Entangled states are essential in basics quantum communication protocols and quantum cry... more ABSTRACT Entangled states are essential in basics quantum communication protocols and quantum cryptography. Ferromagnetic contacts can work as a spin detector, giving possibility of converting information about electron spin to the electric charge, and therefore, detection of entangled states with the electric current measurements is possible. Method of con rming entanglement with non-ideal detectors is presented, the impact of decoherence and noise on states and quality of entanglement is discussed. Entanglement witness (EW) operator method is compared with the CHSH inequalities approach. Required spin polarization for the EW is lower than for the CHSH inequalities. System with asymmetric spin polarizations of detectors was analyzed, including the CHSH inequalities and the EW method.
The extended Hubbard model in the zero-bandwidth limit is studied. The effective Hamiltonian cons... more The extended Hubbard model in the zero-bandwidth limit is studied. The effective Hamiltonian consists of (i) on-site U interaction and intersite (ii) density-density interaction W and (iii) Isinglike magnetic exchange interaction J (between the nearest-neighbors). We present rigorous (and analytical) results obtained within the transfer-matrix method for 1D-chain in two particular cases: (a) W = 0 and n = 1; (b) U → +∞ and n = 1/2 (W = 0, J = 0). We obtain the exact formulas for the partition functions which enables to calculate thermodynamic properties such as entropy, specific heat (c), and double occupancy per site. In both cases the system exhibits an interesting temperature dependence of c involving a characteristic two-peak structure. There are no phase transitions at finite temperatures and the only transitions occur in the ground state. PACS numbers: 71.10.Fd -Lattice fermion models (Hubbard model, etc.) 71.10.-w -Theories and models of many-electron systems 71.10.Hf -Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems 71.45.Lr -Charge-density-wave systems 75.30.Fv -Spin-density waves
We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox,... more We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox, which violates CHSH inequality up to maximal algebraic bound, and second is so called random access code (RAC). The latter is a functionality that enables Bob (receiver) to choose one of two bits of Alice. It has been known, that PR-box supplemented with one bit of communication can be used to simulate RAC. We ask the converse question: to what extent RAC can simulate PR-box? To this end we introduce racbox: a box such that supplemented with one bit of communication offers RAC. As said, PR-box can simulate racbox. The question we raise, is whether any racbox can simulate PR-box. We show that a non-signaling racbox indeed can simulate PR-box, hence those two resources are equivalent. We also provide an example of signalling racbox which cannot simulate PR-box. We give a resource inequality between racbox es and PR-boxes, and show that it is saturated.
We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox,... more We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox, which violates CHSH inequality up to maximal algebraic bound, and second is so called random access code (RAC). The latter is a functionality that enables Bob (receiver) to choose one of two bits of Alice. It has been known, that PR-box supplemented with one bit of communication can be used to simulate RAC. We ask the converse question: to what extent RAC can simulate PR-box? To this end we introduce racbox: a box such that supplemented with one bit of communication offers RAC. As said, PR-box can simulate racbox. The question we raise, is whether any racbox can simulate PR-box. We show that a non-signaling racbox indeed can simulate PR-box, hence those two resources are equivalent. We also provide an example of signalling racbox which cannot simulate PR-box. We give a resource inequality between racboxes and PR-boxes, and show that it is saturated.
Contextuality is central to both the foundations of quantum theory and to the novel information p... more Contextuality is central to both the foundations of quantum theory and to the novel information processing tasks. Although it was recognized before Bell's nonlocality, despite some recent proposals, it still faces a fundamental problem: how to quantify its presence? In this work, we provide a framework for quantifying contextuality. We conduct two complementary approaches: (i) bottom-up approach, where we introduce a communication game, which grasps the phenomenon of contextuality in a quantitative manner; (ii) top-down approach, where we just postulate two measures -relative entropy of contextuality and contextuality cost, analogous to existent measures of non-locality (a special case of contextuality). We then match the two approaches, by showing that the measure emerging from communication scenario turns out to be equal to the relative entropy of contextuality. We give analytical formulas for the proposed measures for some contextual systems. Furthermore we explore properties of these measures such as monotonicity or additivity. arXiv:1209.3745v3 [quant-ph]
The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via ... more The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via simultaneous ac-calorimetry and electrical resistivity measurements. Two successive structural phase transition temperatures, T1 = 125 K and T2 = 110 K, are found to decrease with increasing pressure. The magnetic ordering transition at TN ∼ 1.9 K decreases monotonically up to 1.7 GPa and disappears discontinuously at Pc ∼ 1.9 GPa, where the structural phase transition at T2 is also suppressed. At Pc, enhancement of the effective mass and residual resistivity are observed. Another probable magnetic phase transition, however, is found to take place at TML ∼0.3 K and smoothly varies even when crossing Pc. Structural phase transitions at ambient pressure were also studied by a single crystal X-ray diffraction measurement. Below T2, a tetragonal lattice distortion with doubling of the unit cell along the c-axis is observed, and thus there are two inequivalent Yb-sites below Pc. These results indicate that one Yb-site, having larger valence configuration and thus smaller Kondo temperature, orders at TN. The other phase transition at TML seems to couple to the crystal structure for T2 < T < T1. YbPd is a unique system exhibiting magnetic orderings in metallic charge-ordered Yb systems.
A simple effective model for a description of magnetically ordered insulators is analysed. The ti... more A simple effective model for a description of magnetically ordered insulators is analysed. The tight binding Hamiltonian consists of the effective on-site interaction (U ) and intersite magnetic exchange interactions (J z , J xy ) between nearest-neighbours. The phase diagrams of this model have been determined within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. We show that, depending on the values of interaction parameters and the electron concentration, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (Fα) and nonordered (NO), but also phase separated states (PSα: Fα-NO).
A simple effective model of charge ordered insulators is studied. The tight binding Hamiltonian c... more A simple effective model of charge ordered insulators is studied. The tight binding Hamiltonian consists of the effective on-site interaction U and the intersite density-density interactions Wij (both: nearest-neighbour and next-nearest-neighbour). In the analysis of the phase diagrams we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. The phase separated states have not been taken into account in previous analyses. Our investigations of two cases of the on-site interaction: attraction (U/(−WQ) = −10) and repulsion (U/(−WQ) = 1.1) show that, depending on the values of the next-nearest-neighbour attraction, the system can exhibit not only homogeneous phases: charge ordered (CO) and nonordered (NO), but also various phase separated states (CO-NO, CO-CO).
ABSTRACT Entangled states are essential in basics quantum communication protocols and quantum cry... more ABSTRACT Entangled states are essential in basics quantum communication protocols and quantum cryptography. Ferromagnetic contacts can work as a spin detector, giving possibility of converting information about electron spin to the electric charge, and therefore, detection of entangled states with the electric current measurements is possible. Method of con rming entanglement with non-ideal detectors is presented, the impact of decoherence and noise on states and quality of entanglement is discussed. Entanglement witness (EW) operator method is compared with the CHSH inequalities approach. Required spin polarization for the EW is lower than for the CHSH inequalities. System with asymmetric spin polarizations of detectors was analyzed, including the CHSH inequalities and the EW method.
The extended Hubbard model in the zero-bandwidth limit is studied. The effective Hamiltonian cons... more The extended Hubbard model in the zero-bandwidth limit is studied. The effective Hamiltonian consists of (i) on-site U interaction and intersite (ii) density-density interaction W and (iii) Isinglike magnetic exchange interaction J (between the nearest-neighbors). We present rigorous (and analytical) results obtained within the transfer-matrix method for 1D-chain in two particular cases: (a) W = 0 and n = 1; (b) U → +∞ and n = 1/2 (W = 0, J = 0). We obtain the exact formulas for the partition functions which enables to calculate thermodynamic properties such as entropy, specific heat (c), and double occupancy per site. In both cases the system exhibits an interesting temperature dependence of c involving a characteristic two-peak structure. There are no phase transitions at finite temperatures and the only transitions occur in the ground state. PACS numbers: 71.10.Fd -Lattice fermion models (Hubbard model, etc.) 71.10.-w -Theories and models of many-electron systems 71.10.Hf -Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems 71.45.Lr -Charge-density-wave systems 75.30.Fv -Spin-density waves
We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox,... more We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox, which violates CHSH inequality up to maximal algebraic bound, and second is so called random access code (RAC). The latter is a functionality that enables Bob (receiver) to choose one of two bits of Alice. It has been known, that PR-box supplemented with one bit of communication can be used to simulate RAC. We ask the converse question: to what extent RAC can simulate PR-box? To this end we introduce racbox: a box such that supplemented with one bit of communication offers RAC. As said, PR-box can simulate racbox. The question we raise, is whether any racbox can simulate PR-box. We show that a non-signaling racbox indeed can simulate PR-box, hence those two resources are equivalent. We also provide an example of signalling racbox which cannot simulate PR-box. We give a resource inequality between racbox es and PR-boxes, and show that it is saturated.
We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox,... more We study a problem of interconvertibility of two supra-quantum resources: one is so called PRbox, which violates CHSH inequality up to maximal algebraic bound, and second is so called random access code (RAC). The latter is a functionality that enables Bob (receiver) to choose one of two bits of Alice. It has been known, that PR-box supplemented with one bit of communication can be used to simulate RAC. We ask the converse question: to what extent RAC can simulate PR-box? To this end we introduce racbox: a box such that supplemented with one bit of communication offers RAC. As said, PR-box can simulate racbox. The question we raise, is whether any racbox can simulate PR-box. We show that a non-signaling racbox indeed can simulate PR-box, hence those two resources are equivalent. We also provide an example of signalling racbox which cannot simulate PR-box. We give a resource inequality between racboxes and PR-boxes, and show that it is saturated.
Contextuality is central to both the foundations of quantum theory and to the novel information p... more Contextuality is central to both the foundations of quantum theory and to the novel information processing tasks. Although it was recognized before Bell's nonlocality, despite some recent proposals, it still faces a fundamental problem: how to quantify its presence? In this work, we provide a framework for quantifying contextuality. We conduct two complementary approaches: (i) bottom-up approach, where we introduce a communication game, which grasps the phenomenon of contextuality in a quantitative manner; (ii) top-down approach, where we just postulate two measures -relative entropy of contextuality and contextuality cost, analogous to existent measures of non-locality (a special case of contextuality). We then match the two approaches, by showing that the measure emerging from communication scenario turns out to be equal to the relative entropy of contextuality. We give analytical formulas for the proposed measures for some contextual systems. Furthermore we explore properties of these measures such as monotonicity or additivity. arXiv:1209.3745v3 [quant-ph]
The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via ... more The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via simultaneous ac-calorimetry and electrical resistivity measurements. Two successive structural phase transition temperatures, T1 = 125 K and T2 = 110 K, are found to decrease with increasing pressure. The magnetic ordering transition at TN ∼ 1.9 K decreases monotonically up to 1.7 GPa and disappears discontinuously at Pc ∼ 1.9 GPa, where the structural phase transition at T2 is also suppressed. At Pc, enhancement of the effective mass and residual resistivity are observed. Another probable magnetic phase transition, however, is found to take place at TML ∼0.3 K and smoothly varies even when crossing Pc. Structural phase transitions at ambient pressure were also studied by a single crystal X-ray diffraction measurement. Below T2, a tetragonal lattice distortion with doubling of the unit cell along the c-axis is observed, and thus there are two inequivalent Yb-sites below Pc. These results indicate that one Yb-site, having larger valence configuration and thus smaller Kondo temperature, orders at TN. The other phase transition at TML seems to couple to the crystal structure for T2 < T < T1. YbPd is a unique system exhibiting magnetic orderings in metallic charge-ordered Yb systems.
A simple effective model for a description of magnetically ordered insulators is analysed. The ti... more A simple effective model for a description of magnetically ordered insulators is analysed. The tight binding Hamiltonian consists of the effective on-site interaction (U ) and intersite magnetic exchange interactions (J z , J xy ) between nearest-neighbours. The phase diagrams of this model have been determined within the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. We show that, depending on the values of interaction parameters and the electron concentration, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (Fα) and nonordered (NO), but also phase separated states (PSα: Fα-NO).
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Papers by W. Kłobus