arXiv subjects

Paweł Mazurek

Publications and source records attributed to Paweł Mazurek.

23 records · Page 2Linked to original sources

arXiv2014

Simple scheme for encoding and decoding a qubit in unknown state for various topological codes

We present a scheme for encoding and decoding an unknown state for CSS codes, based on syndrome measurements. We illustrate our method by means of Kitaev toric code, defected-lattice code, topological subsystem code and Haah 3D code. The protocol is local whenever in a given code the crossings between the logical operators consist of next neighbour pairs, which holds for the above codes. For subsystem code we also present scheme in a noisy case, where we allow for bit and phase-flip errors on qubits as well as state preparation and syndrome measurement errors. Similar scheme can be built for two other codes. We show that the fidelity of the protected qubit in the noisy scenario in a large code size limit is of $1-\mathcal{O}(p)$, where $p$ is a probability of error on a single qubit. Regarding Haah code we provide noiseless scheme, leaving the noisy case as an open problem.

quant-ph↗

arXiv2014

Can communication power of separable correlations exceed that of entanglement resource?

The scenario of remote state preparation with shared correlated quantum state and one bit of forward communication [B. Dakic et al. Nature Physics 8, 666-670 (2012)] is considered. The transmission efficiency is examined by considering general encoding and decoding strategies. The importance of use of linear fidelity is recognized. It is shown that separable states cannot exceed the efficiency of entangled states in this protocol. It is proven however that such a surprising phenomena may naturally occur when the decoding agent has limited resources in the sense that either (i) has no information about the coordinates in the sender plane being in question or (ii) is forced to use bistochastic operations only which may be imposed by physically inconvenient local thermodynamical conditions.

quant-ph↗

arXiv2014

The decay of quantum correlations between quantum dot spin qubits and the characteristics of its magnetic field dependence

We address the question of the role of quantum correlations beyond entanglement in context of quantum magnetometry. To this end, we study the evolution of the quantum discord, measured by the rescaled discord, of two electron-spin qubits interacting with an environment of nuclear spins via the hyperfine interaction. We have found that depending on the initial state the evolution can or cannot display indifferentiability points in its time-evolution (due to the energy conservation law), as well as non-trivial dependence on inter-qubit phase. Furthermore, we show that for initial Bell states, quantum correlations display a strong magnetic-field sensitivity which can be utilized for decoherence-driven measurements of the external magnetic field. The potential discord-based measurement is sensitive to a wider range of magnetic field values than the entanglement-based measurement. In principle, entanglement is not a necessary resource for reliable decoherence-driven measurement, while the presence of quantum correlations beyond entanglement is.

quant-ph↗

arXiv2013

Sensitivity of the decay of entanglement of quantum dot spin qubits to the magnetic field

We study the decay of entanglement of quantum dot electron-spin qubits under hyperfine interaction mediated decoherence. We show that two qubit entanglement of a single entangled initial state may exhibit decay characteristic of the two disentanglement regimes in a single sample, when the external magnetic field is changed. The transition is manifested by the supression of time-dependent entanglement oscillations which are superimposed on the slowly varying entanglement decay related to phase decoherence (which result in oscillatory behaviour of entanglement sudden death time as a function of the magnetic field). This unique behaviour allows us to propose the double quantum dot two-electron spin Bell state as a promising candidate for precise measurements of the magnetic field.

quant-ph↗

arXiv2013

Anomalous decay of quantum correlations of quantum dot qubits

We study the evolution of quantum correlations, quantified by the geometric discord, of two excitonic quantum dot qubits under the influence of the phonon environment. We show that the decay of these correlations differs substantially form the decay of entanglement. Instead of displaying sudden death type behavior, the geometric discord shows a tendency to undergo transitions between different types of decay, is sensitive to non-local phase factors, and may already be enhanced by weak environment-mediated interactions. Hence, two-qubit quantum correlations are more robust under decoherence processes, while showing a richer and more complex spectrum of behavior under unitary and non-unitary evolution.

quant-ph↗