Igor Jex
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View article: Unitary generation of GHZ states
Unitary generation of GHZ states Open
Entangled states represent fascinating elements of quantum mechanics and quantum technology. Their generation is an interesting problem combining many techniques developed in quantum optics. Using algebraic properties of special transforms…
View article: Quantum Buridan’s ass
Quantum Buridan’s ass Open
The interplay between symmetry and dynamics is central to physics, as well as to other branches of science. An interesting situation arises in decision-making when you are offered several equally viable solutions and you are forced to sele…
View article: Quantum metrology in a nonlinear-interferometer with feedback
Quantum metrology in a nonlinear-interferometer with feedback Open
In this paper, we propose a nonlinear interferometer with feedback loops and explore its efficiency for phase estimation. We analyse two feedback schemes, one where both modes of the interferometer are fed-back into the device and another …
View article: Recurrence in discrete-time quantum stochastic walks
Recurrence in discrete-time quantum stochastic walks Open
Interplay between quantum interference and classical randomness can enhance performance of various quantum information tasks. In the present paper we analyze recurrence phenomena in the discrete-time quantum stochastic walk on a line, whic…
View article: Boson Sampling from Non-Gaussian States
Boson Sampling from Non-Gaussian States Open
Boson sampling has emerged as an important tool to demonstrate the difference between quantum and classical computers and has attracted the interest of experimentalists and theoreticians. In this work we study Boson sampling from general, …
View article: Unambiguous preparation of Bell pairs
Unambiguous preparation of Bell pairs Open
The ability of preparing perfect Bell pairs with a practical scheme is of great relevance for quantum communication as well as distributed quantum computing. We propose a scheme which probabilistically, but unambiguously produces the $\lef…
View article: Robustness of chaotic behavior in iterated quantum protocols
Robustness of chaotic behavior in iterated quantum protocols Open
One of the simplest possible quantum circuits, consisting of a CNOT gate, a Hadamard gate and a measurement on one of the outputs is known to lead to chaotic dynamics when applied iteratively on an ensemble of equally prepared qubits. The …
View article: Jaynes principle for quantum Markov processes: Generalized Gibbs - von Neumann states rule
Jaynes principle for quantum Markov processes: Generalized Gibbs - von Neumann states rule Open
We prove that any asymptotics of a finite-dimensional quantum Markov processes can be formulated in the form of a generalized Jaynes principle in the discrete as well as in the continuous case. Surprisingly, we find that the open system dy…
View article: Asymptotic phase-locking and synchronization in two-qubit systems
Asymptotic phase-locking and synchronization in two-qubit systems Open
The paper concerns spontaneous asymptotic phase-locking and synchronization in two-qubit systems undergoing continuous Markovian evolution described by Lindbladian dynamics with normal Lindblad operators. Using analytic methods, all phase-…
View article: Asymptotic phase-locking and synchronization in two-qubit systems
Asymptotic phase-locking and synchronization in two-qubit systems Open
The paper concerns spontaneous asymptotic phase-locking and synchronization in two-qubit systems undergoing continuous Markovian evolution described by Lindbladian dynamics with normal Lindblad operators. Using analytic methods, all phase-…
View article: Key graph properties affecting transport efficiency of flip-flop Grover percolated quantum walks
Key graph properties affecting transport efficiency of flip-flop Grover percolated quantum walks Open
Quantum walks exhibit properties without classical analogues. One of those is the phenomenon of asymptotic trapping -- there can be non-zero probability of the quantum walker being localised in a finite part of the underlying graph indefin…
View article: Key graph properties affecting transport efficiency of flip-flop Grover percolated quantum walks
Key graph properties affecting transport efficiency of flip-flop Grover percolated quantum walks Open
Quantum walks exhibit properties without classical analogues. One of those is the phenomenon of asymptotic trapping -- there can be non-zero probability of the quantum walker being localised in a finite part of the underlying graph indefin…
View article: Iterated nth order nonlinear quantum dynamics with mixed initial states
Iterated nth order nonlinear quantum dynamics with mixed initial states Open
Nonlinear quantum transformations play an important role in quantum state distillation, aiding quantum communication schemes. The simplest of these involve quadratic rational maps for qubits, higher order versions have not been explored in…
View article: Relaxation to equilibrium in controlled-not quantum networks
Relaxation to equilibrium in controlled-not quantum networks Open
The approach to equilibrium of quantum mechanical systems is a topic as old\nas quantum mechanics itself, but has recently seen a surge of interest due to\napplications in quantum technologies, including, but not limited to, quantum\ncompu…
View article: Local Versus Global Two-Photon Interference in Quantum Networks
Local Versus Global Two-Photon Interference in Quantum Networks Open
We devise an approach to characterizing the intricate interplay between classical and quantum interference of two-photon states in a network, which comprises multiple time-bin modes. By controlling the phases of delocalized single photons,…
View article: Complete classification of trapping coins for quantum walks on the two-dimensional square lattice
Complete classification of trapping coins for quantum walks on the two-dimensional square lattice Open
One of the unique features of discrete-time quantum walks is called trapping, meaning the inability of the quantum walker to completely escape from its initial position, although the system is translationally invariant. The effect is depen…
View article: Counterintuitive role of geometry in transport by quantum walks
Counterintuitive role of geometry in transport by quantum walks Open
Quantum walks are accepted as a generic model for quantum transport. The\ncharacter of the transport crucially depends on the properties of the walk like\nits geometry and the driving coin. We demonstrate that increasing transport\ndistanc…
View article: Quantum walk transport on carbon nanotube structures
Quantum walk transport on carbon nanotube structures Open
View article: Deterministic twirling with low resources
Deterministic twirling with low resources Open
View article: Detailed study of Gaussian boson sampling
Detailed study of Gaussian boson sampling Open
Since the development of Boson sampling, there has been a quest to construct\nmore efficient and experimentally feasible protocols to test the computational\ncomplexity of sampling from photonic states. In this paper we interpret and\nexte…
View article: Percolated quantum walks with a general shift operator: From trapping to transport
Percolated quantum walks with a general shift operator: From trapping to transport Open
We present a generalized definition of discrete-time quantum walks convenient for capturing a rather broad spectrum of walker's behavior on arbitrary graphs. It includes and covers both: the geometry of possible walker's positions with int…
View article: Phase transition in iterated quantum protocols for noisy inputs
Phase transition in iterated quantum protocols for noisy inputs Open
Quantum information processing exploits all the features quantum mechanics offers. Among them there is the possibility to induce nonlinear maps on a quantum system by involving two or more identical copies of the given system in the same s…
View article: A photonic quantum walk with a four-dimensional coin
A photonic quantum walk with a four-dimensional coin Open
The dimensionality of the internal coin space of discrete-time quantum walks has a strong impact on the complexity and richness of the dynamics of quantum walkers. While two-dimensional coin operators are sufficient to define a certain ran…
View article: Sensitivity to initial noise in measurement-induced nonlinear quantum dynamics
Sensitivity to initial noise in measurement-induced nonlinear quantum dynamics Open
We consider a special iterated quantum protocol with measurement-induced nonlinearity for qubits, where all pure initial states on the Bloch sphere can be considered chaotic. The dynamics is ergodic with no attractive fixed cycles. We show…
View article: Sensitivity to initial noise in measurement-induced nonlinear quantum\n dynamics
Sensitivity to initial noise in measurement-induced nonlinear quantum\n dynamics Open
We consider a special iterated quantum protocol with measurement-induced\nnonlinearity for qubits, where all pure initial states on the Bloch sphere can\nbe considered chaotic. The dynamics is ergodic with no attractive fixed cycles.\nWe s…
View article: Quantum Markov processes: From attractor structure to explicit forms of asymptotic states
Quantum Markov processes: From attractor structure to explicit forms of asymptotic states Open
View article: Probing measurement-induced effects in quantum walks via recurrence
Probing measurement-induced effects in quantum walks via recurrence Open
The effects of projective measurements on the quantum mechanical evolution of a particle can be simulated with coherent light.
View article: Gaussian Boson Sampling
Gaussian Boson Sampling Open
Boson sampling has emerged as a tool to explore the advantages of quantum over classical computers as it does not require universal control over the quantum system, which favors current photonic experimental platforms. Here, we introduce G…
View article: Driven Boson Sampling
Driven Boson Sampling Open
Sampling the distribution of bosons that have undergone a random unitary evolution is strongly believed to be a computationally hard problem. Key to outperforming classical simulations of this task is to increase both the number of input p…
View article: Limit Density of 2D Quantum Walk: Zeroes of the Weight Function
Limit Density of 2D Quantum Walk: Zeroes of the Weight Function Open
Properties of the probability distribution generated by a discrete-time quantum walk, such as the number of peaks it contains, depend strongly on the choice of the initial condition. In the present paper we discuss from this point of view …