Waldemar Klobus - Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland

Waldemar Klobus
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Name
Waldemar Klobus
Affiliation
Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland
City
Poznań
Country
Poland

Pubs By Year

Pub Categories

 
Quantum Physics (10)
 
Physics - Strongly Correlated Electrons (4)
 
Physics - Statistical Mechanics (2)
 
Physics - Other (2)
 
General Relativity and Quantum Cosmology (1)
 
Physics - Mesoscopic Systems and Quantum Hall Effect (1)
 
Mathematics - Mathematical Physics (1)
 
Mathematical Physics (1)

Publications Authored By Waldemar Klobus

One of the formulations of Heisenberg uncertainty principle, concerning so-called measurement uncertainty, states that the measurement of one observable modifies the statistics of the other. Here, we derive such a measurement uncertainty principle from two comprehensible assumptions: impossibility of instantaneous messaging at a distance (no-signaling), and violation of Bell inequalities (non-locality). The uncertainty is established for a pair of observables of one of two spatially separated systems that exhibit non-local correlations. Read More

Heisenberg uncertainty principle is a trademark of quantum mechanics. In its original form it states that one cannot gain information about a system without disturbing it, which is a core of novel cryptographic techniques based on quantum effects. The principle can be derived from mathematical formalism of quantum theory. Read More

The uncertainty principle, which states that certain sets of quantum-mechanical measurements have a minimal joint uncertainty, has many applications in quantum cryptography. But in such applications, it is important to consider the effect of a (sometimes adversarially controlled) memory that can be correlated with the system being measured: The information retained by such a memory can in fact diminish the uncertainty of measurements. Uncertainty conditioned on a memory was considered in the past by Berta et al. Read More

We present a unified axiomatic approach to contextuality and non-locality based on the fact that both are resource theories. In those theories the main objects are consistent boxes, which can be transformed by certain operations to achieve certain tasks. The amount of resource is quantified by appropriate measures of the resource. Read More

2015May
Affiliations: 1Adam Mickiewicz University in Poznań, Poznań, Poland, 2Adam Mickiewicz University in Poznań, Poznań, Poland, 3Adam Mickiewicz University in Poznań, Poznań, Poland

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) Ising-like 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) $U\rightarrow+\infty$ and $n=1/2$ ($W\neq 0$, $J\neq 0$). Read More

In any theory satisfying the no-signaling principle correlations generated among spatially separated parties in a Bell-type experiment are subject to certain constraints known as monogamy relations. Recently, in the context of the black hole information loss problem it was suggested that these monogamy relations might be violated. This in turn implies that correlations arising in such a scenario must violate the no-signaling principle and hence can be used to send classical information between parties. Read More

We investigate theoretically the use of non-ideal ferromagnetic contacts as a mean to detect quantum entanglement of electron spins in transport experiments. We use a designated entanglement witness and find a minimal spin polarization of $\eta > 1/\sqrt{3} \approx 58 %$ required to demonstrate spin entanglement. This is significantly less stringent than the ubiquitous tests of Bell's inequality with $\eta > 1/\sqrt[4]{2}\approx 84%$. Read More

We study a problem of interconvertibility of two supra-quantum resources: one is so called PR-box, 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. Read More

We conjecture new uncertainty relations which restrict correlations between results of measurements performed by two separated parties on a shared quantum state. The first uncertainty relation bounds the sum of two mutual informations when one party measures a single observable and the other party measures one of two observables. The uncertainty relation does not follow from Maassen-Uffink uncertainty relation and is much stronger than Hall uncertainty relation derived from the latter. Read More

We consider multiple entanglement swappings performed on a chain of bipartite states. Each state does not violate CHSH inequality. We show that before some critical number of entanglement swappings is achieved the output state does not violate this inequality either. Read More

2011Aug
Affiliations: 1Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 2Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 3Faculty of Physics, Adam Mickiewicz University, Poznań, Poland

A simple effective model of charge ordered and (or) magnetically ordered insulators is studied. The tight binding Hamiltonian analyzed consists of (i) the effective on-site interaction U, (ii) the intersite density-density interaction W and (iii) intersite magnetic exchange interaction Jz (or Jxy) between nearest-neighbors. The intersite interaction are treated within the mean-field approximation. Read More

We show that recent results on the interaction of causality-respecting particles with particles on closed timelike curves derived in [Phys. Rev. A 82, 062330 (2010)] depend on ambiguous assumption about the form of the state which is inputted into the proposed equivalent circuit. Read More

2010Jul
Affiliations: 1Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 2Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 3Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland

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 (Jz, Jxy) 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. Read More

2010Apr
Affiliations: 1Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 2Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland, 3Electron States of Solids Division, Faculty of Physics, Adam Mickiewicz University, Poznań, Poland

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. Read More