Elementary gates for quantum information with superposed coherent states (2010)
Marek, Petr, Fiurasek, Jaromir
We propose a new way of implementing several elementary quantum gates for qubits in the coherent state basis. The operations are probabilistic and employ single photon subtractions as the driving...
Direct experimental verification of quantum commutation relations for Pauli operators (2010)
Yao, Xing-Can, Fiurasek, Jaromir, Lu, He, Gao, Wei-Bo, Chen, Yu-Ao, Chen, Zeng-Bing, ...
We propose and demonstrate scheme for direct experimental testing of quantum commutation relations for Pauli operators. The implemented device is an advanced quantum processor that involves two...
Cernoch, Antonin, Soubusta, Jan, Celechovska, Lucie, Dusek, Miloslav, Fiurasek, Jaromir
We report on experimental implementation of the optimal universal asymmetric 1->2 quantum cloning machine for qubits encoded into polarization states of single photons. Our linear optical machine...
We propose and investigate an optical scheme for probabilistic implementation of an arbitrary single-mode quantum operation that can be expressed as a function of photon number operator. The scheme...
Optimal two-copy discrimination of quantum measurements (2009)
Fiurasek, Jaromir, Micuda, Michal
We investigate optimal discrimination between two projective quantum measurements on a single qubit. We consider scenario where the measurement that should be identified can be performed twice and we...
Experimental demonstration of teleportation-based programmable quantum gate (2009)
Slodicka, Lukas, Jezek, Miroslav, Fiurasek, Jaromir
We experimentally demonstrate a programmable quantum gate that applies a sign flip operation to data qubit in an arbitrary basis fully specified by the quantum state of a two-qubit program register....
Markov Chain Monte Carlo Estimation of Quantum States (2009)
DiGuglielmo, James, Messenger, Chris, Fiurasek, Jaromir, Hage, Boris, Samblowski, Aiko, Schmidt, Tabea, ...
We apply a Bayesian data analysis scheme known as the Markov Chain Monte Carlo (MCMC) to the tomographic reconstruction of quantum states. This method yields a vector, known as the Markov chain,...
Experimental realization of programmable quantum gate (2008)
Micuda, Michal, Jezek, Miroslav, Dusek, Miloslav, Fiurasek, Jaromir
We experimentally demonstrate a programmable single-qubit quantum gate. This device applies a unitary phase shift operation to a data qubit with the value of the phase shift being fully determined by...
Preparation of distilled and purified continuous variable entangled states (2008)
Hage, Boris, Samblowski, Aiko, DiGuglielmo, James, Franzen, Alexander, Fiurasek, Jaromir, Schnabel, Roman
The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to...
Conditional preparation of arbitrary atomic Dicke states (2008)
Lemr, Karel, Fiurasek, Jaromir
We propose an experimentally accessible procedure for conditional preparation of highly non-classical states of collective spin of an atomic ensemble. The quantum state engineering is based on a...
A No-Go Theorem for Gaussian Quantum Error Correction (2008)
Niset, Julien, Fiurasek, Jaromir, Cerf, Nicolas J.
It is proven that Gaussian operations are of no use for protecting Gaussian states against Gaussian errors in quantum communication protocols. Specifically, we introduce a new quantity characterizing...
Experimental asymmetric phase-covariant quantum cloning of polarization qubits (2008)
Soubusta, Jan, Bartuskova, Lucie, Cernoch, Antonin, Dusek, Miloslav, Fiurasek, Jaromir
We report on two optical realizations of the $1 \to 2$ asymmetric phase-covariant cloning machines for polarization states of single photons. The experimental setups combine two-photon interference...
Linear optical Fredkin gate based on partial-SWAP gate (2008)
We propose a scheme for linear optical quantum Fredkin gate based on the combination of recently experimentally demonstrated linear optical partial SWAP gate and controlled-Z gates. Both heralded...
Preparation of distilled and purified continuous-variable entangled states (2008)
Hage, Boris, Samblowski, Aiko, DiGuglielmo, James, Franzen, Alexander, Fiurasek, Jaromir, Schnabel, Roman
The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to...
Quantum cloning a pair of orthogonally polarized photons with linear optics (2007)
Fiurasek, Jaromir, Cerf, Nicolas J.
A linear optical probabilistic scheme for the optimal cloning of a pair of orthogonally-polarized photons is devised, based on single- and two-photon interferences. It consists in a partial...
Preparation of entangled states of two photons in several spatial modes (2007)
Lemr, Karel, Fiurasek, Jaromir
We describe a protocol capable of preparing an arbitrary state of two photons in several spatial modes using pairs of photons generated by spontaneous parametric down-conversion, linear optical...
Multiple copy distillation and purification of phase diffused squeezed states (2007)
Marek, Petr, Fiurasek, Jaromir, Hage, Boris, Franzen, Alexander, DiGugliemo, James, Schnabel, Roman
We provide a detailed theoretical analysis of multiple copy purification and distillation protocols for phase diffused squeezed states of light. The standard iterative distillation protocol is...
Experimental characterization of Gaussian quantum communication channels (2007)
DiGuglielmo, James, Hage, Boris, Franzen, Alexander, Fiurasek, Jaromir, Schnabel, Roman
We present a full experimental characterization of continuous variable quantum communication channels established by shared entanglement together with local operations and classical communication....
Gaussian localizable entanglement (2007)
Fiurasek, Jaromir, Mista Jr, Ladislav
We investigate localization of entanglement of multimode Gaussian states into a pair of modes by local Gaussian measurements on the remaining modes and classical communication. We find that for pure...
On the distillation and purification of phase-diffused squeezed states (2007)
Hage, Boris, Franzen, Alexander, DiGuglielmo, James, Marek, Petr, Fiurasek, Jaromir, Schnabel, Roman
Recently it was discovered that non-Gaussian decoherence processes, such as phase-diffusion, can be counteracted by purification and distillation protocols that are solely built on Gaussian...
Experimental characterization of Gaussian quantum communication channels (2007)
DiGuglielmo, James, Hage, Boris, Franzen, Alexander, Fiurasek, Jaromir, Schnabel, Roman
We present a full experimental characterization of continuous variable quantum communication channels established by shared entanglement together with local operations and classical communication....
Experimentally feasible purification of continuous-variable entanglement (2007)
Fiurasek, Jaromir, Marek, Petr, Filip, Radim, Schnabel, Roman
We propose a scheme for purification and distillation of squeezed and entangled continuous-variable states of light transmitted through a channel exhibiting phase fluctuations. The outstanding...
Multiple-copy distillation and purification of phase-diffused squeezed states (2007)
Marek, Petr, Fiurasek, Jaromir, Hage, Boris, Franzen, Alexander, DiGuglielmo, James, Schnabel, Roman
We provide a detailed theoretical analysis of multiple-copy purification and distillation protocols for phase-diffused squeezed states of light. The standard iterative distillation protocol is...
Fibre-optics implementation of asymmetric phase-covariant quantum cloner (2006)
Bartuskova, Lucie, Dusek, Miloslav, Cernoch, Antonin, Soubusta, Jan, Fiurasek, Jaromir
We present the experimental realization of optimal symmetric and asymmetric phase-covariant 1->2 cloning of qubit states using fiber optics. State of each qubit is encoded into a single photon which...
Optimal multicopy asymmetric Gaussian cloning of coherent states (2006)
Fiurasek, Jaromir, Cerf, Nicolas J.
We investigate the asymmetric Gaussian cloning of coherent states which produces M copies from N input replicas, such that the fidelity of all copies may be different. We show that the optimal...
Optimal probabilistic estimation of quantum states (2006)
We extend the concept of probabilistic unambiguous discrimination of quantum states to quantum state estimation. We consider a scenario where the measurement device can output either an estimate of...
Optimal partial estimation of quantum states from several copies (2006)
Mista Jr., Ladislav, Fiurasek, Jaromir
We derive analytical formula for the optimal trade-off between the mean estimation fidelity and the mean fidelity of the qubit state after a partial measurement on N identically prepared qubits. We...
Optical implementation of the encoding of two qubits to a single qutrit (2006)
Bartuskova, Lucie, Cernoch, Antonin, Filip, Radim, Fiurasek, Jaromir, Soubusta, Jan, Dusek, Miloslav
We have devised an optical scheme for the recently proposed protocol for encoding two qubits into one qutrit. In this protocol, Alice encodes an arbitrary pure product state of two qubits into a...
Linear optics quantum Toffoli and Fredkin gates (2006)
We design linear optics multiqubit quantum logic gates. We assume the traditional encoding of a qubit onto state of a single photon in two modes (e.g. spatial or polarization). We suggest schemes...
Experimental Demonstration of Continuous Variable Purification of Squeezed States (2006)
Franzen, Alexander, Hage, Boris, DiGuglielmo, James, Fiurasek, Jaromir, Schnabel, Roman
We report on the first experimental demonstration of purification of nonclassical continuous variable states. The protocol uses two copies of phase-diffused states overlapped on a beam splitter and...
Optical Quantum Cloning - a Review (2005)
Cerf, Nicolas J., Fiurasek, Jaromir
After a brief introduction to the quantum no-cloning theorem and its link with the linearity and causality of quantum mechanics, the concept of quantum cloning machines is sketched, following,...
Experimental purification of coherent states (2005)
Andersen, Ulrik L., Filip, Radim, Fiurasek, Jaromir, Josse, Vincent, Leuchs, Gerd
We propose a scheme for optimal Gaussian purification of coherent states from several imperfect copies. The proposal is experimentally demonstrated for the case of two copies of a coherent state sent...
Highly asymmetric quantum cloning in arbitrary dimension (2005)
Fiurasek, Jaromir, Filip, Radim, Cerf, Nicolas J.
We investigate the universal asymmetric cloning of states in a Hilbert space of arbitrary dimension. We derive the class of optimal and fully asymmetric 1->3 cloners, which produce three copies, each...
Fiurasek, Jaromir, Garcia-Patron, Raul, Cerf, Nicolas J.
We propose a scheme for the conditional generation of arbitrary finite superpositions of (squeezed) Fock states in a single mode of a traveling optical field. The suggested setup requires only a...
Economical quantum cloning in any dimension (2004)
Durt, Thomas, Fiurasek, Jaromir, Cerf, Nicolas J.
The possibility of cloning a d-dimensional quantum system without an ancilla is explored, extending on the economical phase-covariant cloning machine found in [Phys. Rev. A {\bf 60}, 2764 (1999)] for...
Experimental demonstration of quantum memory for light (2004)
Julsgaard,Brian, Sherson,Jacob, Cirac,J. Ignacio, Fiurasek,Jaromir, Polzik,Eugene S.
Experimental demonstration of quantum memory for light (2004)
Julsgaard, Brian, Sherson, Jacob, Cirac, J. Ignacio, Fiurasek, Jaromir, Polzik, Eugene S.
The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot, even in principle, be...
Fiurasek, Jaromir, Cerf, Nicolas J., Polzik, Eugene S.
A scheme for the optimal Gaussian cloning of coherent light states at the light-atoms interface is proposed. The distinct feature of this proposal is that the clones are stored in an atomic quantum...
Optimal probabilistic cloning and purification of quantum states (2004)
We investigate the probabilistic cloning and purification of quantum states. The performance of these probabilistic operations is quantified by the average fidelity between the ideal and actual...
Soubusta, Jan, Cernoch, Antonin, Fiurasek, Jaromir, Dusek, Miloslav
We present an optical implementation of two programmable quantum measurement devices. The first one serves for unambiguous discrimination of two nonorthogonal states of a qubit. The particular pair...
Experimental demonstration of quantum memory for light (2004)
Julsgaard, Brian, Sherson, Jacob, Cirac, J. Ignacio, Fiurasek, Jaromir, Polzik, Eugene S.
How to measure squeezing and entanglement of Gaussian states without homodyning (2003)
Fiurasek, Jaromir, Cerf, Nicolas J.
We propose a scheme for measuring the squeezing, purity, and entanglement of Gaussian states of light that does not require homodyne detection. The suggested setup only needs beam splitters and...
Probabilistic quantum multimeters (2003)
Fiurasek, Jaromir, Dusek, Miloslav
We propose quantum devices that can realize probabilistically different projective measurements on a qubit. The desired measurement basis is selected by the quantum state of a program register. First...
Unitary Gate Synthesis for Continuous Variable Systems (2003)
We investigate the synthesis of continuous-variable two-mode unitary gates in the setting where two modes A and B are coupled by a fixed quadratic Hamiltonian H. The gate synthesis consists of a...
Cloning the entanglement of a pair of quantum bits (2003)
Lamoureux, Louis-Philippe, Navez, Patrick, Fiurasek, Jaromir, Cerf, Nicolas J.
It is shown that any quantum operation that perfectly clones the entanglement of all maximally-entangled qubit pairs cannot preserve separability. This ``entanglement no-cloning'' principle naturally...
Entanglement generation in continuously coupled parametric generators (2003)
Herec, Jiri, Fiurasek, Jaromir, Mista Jr, Ladislav
We investigate a compact source of entanglement. This device is composed of a pair of linearly coupled nonlinear waveguides operating by means of degenerate parametric downconversion. For the vacuum...
Quantum inference of states and processes (2002)
Jezek, Miroslav, Fiurasek, Jaromir, Hradil, Zdenek
The maximum-likelihood principle unifies inference of quantum states and processes from experimental noisy data. Particularly, a generic quantum process may be estimated simultaneously with unknown...
Optimal discrimination of mixed quantum states involving inconclusive results (2002)
Fiurasek, Jaromir, Jezek, Miroslav
We propose a generalized discrimination scheme for mixed quantum states. In the present scenario we allow for certain fixed fraction of inconclusive results and we maximize the success rate of the...
Simple optical measurement of the overlap and fidelity of quantum states: An experiment (2002)
Hendrych, Martin, Dusek, Miloslav, Filip, Radim, Fiurasek, Jaromir
We present the experimental results of measurements of the overlap of both pure and mixed polarization states of photons. The fidelity and purity of mixed states were also measured. The experimental...
Entanglement concentration of continuous variable quantum states (2002)
Fiurasek, Jaromir, Mista, Ladislav, Jr., Filip, Radim
We propose two probabilistic entanglement concentration schemes for a single copy of two-mode squeezed vacuum state. The first scheme is based on the off-resonant interaction of a Rydberg atom with...
Gaussian transformations and distillation of entangled Gaussian states (2002)
We prove that it is impossible to distill more entanglement from a single copy of a two-mode bipartite entangled Gaussian state via LOCC Gaussian operations. More generally, we show that any...
Universal measurement apparatus controlled by quantum software (2002)
Fiurasek, Jaromir, Dusek, Miloslav, Filip, Radim
We propose a quantum device that can approximate any projective measurement on a qubit. The desired measurement basis is selected by the quantum state of a "program register". The device is optimized...
Improving fidelity of continuous-variable teleportation via local operations (2002)
We study the Braunstein-Kimble setup for teleportation of quantum state of a single mode of optical field. We assume that the sender and receiver share a two-mode Gaussian state and we identify...
Continuous-variable Werner state: separability, nonlocality, squeezing and teleportation (2001)
Mista Jr., Ladislav, Filip, Radim, Fiurasek, Jaromir
We investigate the separability, nonlocality and squeezing of continuous-variable analogue of the Werner state: a mixture of pure two-mode squeezed vacuum state with local thermal radiations....
Structural physical approximations of unphysical maps and generalized quantum measurements (2001)
We investigate properties of the structural physical approximation (SPA) of the partial transposition map recently introduced by Horodecki and Ekert [quant-ph/0111064]. We focus on the case of...
Conditional generation of N-photon entangled states of light (2001)
We propose a scheme for conditional generation of two-mode N-photon path-entangled states of traveling light field. These states may find applications in quantum optical lithography and they may be...
Extremal equation for optimal completely-positive maps (2001)
We derive an extremal equation for optimal completely-positive map which most closely approximates a given transformation between pure quantum states. Moreover, we also obtain an upper bound on the...
Bell-inequality violation with "thermal" radiation (2001)
Filip, Radim, Dusek, Miloslav, Fiurasek, Jaromir, Mista, Ladislav
The model of a quantum-optical device for a conditional preparation of entangled states from input mixed states is presented. It is demonstrated that even thermal or pseudo-thermal radiation can be...
A simple scheme for conditional generation of nonclassical light with sub-Poissonian photon-number statistics is proposed. The method utilizes entanglement of signal and idler modes in two-mode...
Comment on "Maximum likelihood reconstruction of CP maps", quant-ph/0009104 (2001)
Fiurasek, Jaromir, Hradil, Zdenek
The treatment proposed by Sacchi quant-ph/0009104 does not represent correct solution, since the necessary conditions on CP maps are not guaranteed.
Maximum-likelihood estimation of quantum measurement (2001)
Maximum likelihood estimation is applied to the determination of an unknown quantum measurement. The measuring apparatus performs measurements on many different quantum states and the positive...
Optical implementation of continuous-variable quantum cloning machines (2000)
We propose an optical implementation of the Gaussian continuous-variable quantum cloning machines. We construct a symmetric N -> M cloner which optimally clones coherent states and we also provide an...
Measurement of quantum devices (2000)
Fiurasek, Jaromir, Hradil, Zdenek
Maximum-likelihood estimation is applied to identification of an unknown quantum mechanical process represented by a ``black box''. In contrast to linear reconstruction schemes the proposed approach...
Sampling functions for multimode homodyne tomography with a single local oscillator (2000)
We derive various sampling functions for multimode homodyne tomography with a single local oscillator. These functions allow us to sample multimode s-parametrized quasidistributions, density matrix...
Direct sampling of exponential phase moments of smoothed Wigner functions (2000)
We investigate exponential phase moments of the s-parametrized quasidistributions (smoothed Wigner functions). We show that the knowledge of these moments as functions of s provides, together with...