Natalia Korolkova - Profile on Academia.edu (original) (raw)

Papers by Natalia Korolkova

We demonstrate a general weak measurement model which allows Gaussian preserving entanglement con... more We demonstrate a general weak measurement model which allows Gaussian preserving entanglement concentration of the two mode squeezed vacuum. The power of this simple and elegant protocol is through the constraints it places on possible ancilla states and measurement strategies that will allow entanglement concentration. In particular, it is shown how previously discovered protocols of this kind emerge as special examples of the general model described here. Finally, as evidence of its utility, we use it to provide another novel example of such a protocol.

In an initially uncorrelated mixed separable bi-partite system, quantum correlations can emerge u... more In an initially uncorrelated mixed separable bi-partite system, quantum correlations can emerge under the action of a local measurement or local noise [A. Streltsov, H. Kampermann, and D. Bruß, Phys. Rev. Lett. 107, 170502 (2011)]. We analyze this counter-intuitive phenomenon using quantum discord as a quantifier. We then relate changes in quantum discord to system-environment correlations between the system in a mixed state and some purifying environmental mode using the Koashi-Winter inequality. On this basis, we suggest an interpretation of discord as a byproduct of transferring entanglement and correlations around the different subsystems of a global pure state.

We suggest and discuss a concept of deterministic integrated source of non-classical light based ... more We suggest and discuss a concept of deterministic integrated source of non-classical light based on the coherent diffusive photonics, a coherent light flow in a system of dissipatively coupled waveguides. We show how this practical quantum device can be realized with a system of single-mode waveguides laser-inscribed in nonlinear glass. We describe a hierarchy of models, from the complete multi-mode model of the waveguide network to the single mode coupled to a bath, analyze the conditions for validity of the simplest single-mode model and demonstrate feasibility of the generation of bright sub-Poissonian light states merely from a coherent input. Notably, the generation of non-classical states occurs at the initial stages of the dynamics, and can be accounted for in the linear model that allows us to circumvent the prohibiting computational complexity of the exact full quantum representation.

Přednaska se týkala výzkumu ve třech oblastech, který probihal ve skupině kvantove optiky na univ... more Přednaska se týkala výzkumu ve třech oblastech, který probihal ve skupině kvantove optiky na univerzitě v St Andrews ve Skotsku: (1) Generovani negaussovských stavů pomoci tzv. Kerrovy nelinearity, (2) koncentrace kvantove provazanosti pomoci slabých měřeni a (3) distribuce provazanosti pomoci separabilniho stavu.

Bright quantum-entangled pulses

Summary form only given. We report on a scheme for the generation of bright entangled light beams... more Summary form only given. We report on a scheme for the generation of bright entangled light beams aimed at quantum communication applications. The experiment is based on the recently proposed theme where two intense independently squeezed light fields interfere to produce multi-photon entangled light fields. An asymmetric fibre Sagnac interferometer is used.

Kerr-effect induced correlations of optical fiber solitons and the impact of phase control

Frontiers in Optics, 2003

1. Summary The non-linear interaction between light pulses and matter depends on the amplitude an... more 1. Summary The non-linear interaction between light pulses and matter depends on the amplitude and phase distribution within the pulse. At equilibrium the non-linear dynamics of optical pulses in fibers produces solitons which are stable in a classical regime. In contrast, the quantum ...

Reconciliation witness and reliability of a quantum atmospheric channel

Physica Scripta, 2013

ABSTRACT The reliability of free-space quantum communication is strongly affected by turbulence p... more ABSTRACT The reliability of free-space quantum communication is strongly affected by turbulence present in atmospheric channels. The signal is randomly distorted or gets lost due to the fluctuations of atmospheric refractive index. We consider quantum communication with coherent and squeezed states and derive the fidelities for quantum states transmitted through such a free-space channel. We show that the fidelity can be significantly enhanced by postselecting high transmission events at the expense of decreasing transmission bit rate. Next, we introduce the witness function that characterizes the reliability of the reconciliation procedure between the communicating parties. Based on this measure, we suggest the receiver strategy that further improves the reconciliation quality.

Formation and conversion of the polarization-squeezed light

Journal of Modern Optics, 1996

We consider polarization-squeezed (PS) light generation in anisotropic Kerr medium. The fluctuati... more We consider polarization-squeezed (PS) light generation in anisotropic Kerr medium. The fluctuations of the Stokes parameter either S2 or S3 are suppressed in PS light. We show the possibility to transform PS light into light with sub-Poissonian statistics by linear conversion (phase plate and analyser). The quantum properties of the second harmonic (SH) generated by frequency doubling of the PS light are investigated.

Physical Review A, 2019

Digital signatures ensure the integrity of a classical message and the authenticity of its sender... more Digital signatures ensure the integrity of a classical message and the authenticity of its sender. Despite their far-reaching use in modern communication, currently used signature schemes rely on computational assumptions and will be rendered insecure by a quantum computer. We present a quantum digital signatures (QDS) scheme whose security is instead based on the impossibility of perfectly and deterministically distinguishing between quantum states. Our continuous-variable (CV) scheme relies on phase measurement of a distributed alphabet of coherent states, and allows for secure message authentication against a quantum adversary performing collective beamsplitter and entangling-cloner attacks. Crucially, for the first time in the CV setting we allow for an eavesdropper on the quantum channels and yet retain shorter signature lengths than previous protocols with no eavesdropper. This opens up the possibility to implement CV QDS alongside existing CV quantum key distribution (QKD) platforms with minimal modification.

Reports on Progress in Physics

In this review we discuss intriguing properties of apparently classical optical fields, that go b... more In this review we discuss intriguing properties of apparently classical optical fields, that go beyond purely classical context and allow us to speak about quantum characteristics of such fields and about their applications in quantum technologies. We briefly define the genuinely quantum concepts of entanglement and steering. We then move to the boarder line between classical and quantum world introducing quantum discord, a more general concept of quantum coherence, and finally a controversial notion of classical entanglement. To unveil the quantum aspects of often classically perceived systems, we focus more in detail on quantum discordant correlations between the light modes and on nonseparability properties of optical vector fields leading to entanglement between different degrees of freedom of a single beam. To illustrate the aptitude of different types of correlated systems to act as quantum or quantum-like resource, entanglement activation from discord, highprecision measurements with classical entanglement and quantum information tasks using intra-system correlations are discussed. The common themes behind the versatile quantum properties of seemingly classical light are coherence, polarization and inter and intra-mode quantum correlations.

Nature communications, Dec 4, 2017

A photonic circuit is generally described as a structure in which light propagates by unitary exc... more A photonic circuit is generally described as a structure in which light propagates by unitary exchange and transfers reversibly between channels. In contrast, the term 'diffusive' is more akin to a chaotic propagation in scattering media, where light is driven out of coherence towards a thermal mixture. Based on the dynamics of open quantum systems, the combination of these two opposites can result in novel techniques for coherent light control. The crucial feature of these photonic structures is dissipative coupling between modes, via an interaction with a common reservoir. Here, we demonstrate experimentally that such systems can perform optical equalisation to smooth multimode light, or act as a distributor, guiding it into selected channels. Quantum thermodynamically, these systems can act as catalytic coherent reservoirs by performing perfect non-Landauer erasure. For lattice structures, localised stationary states can be supported in the continuum, similar to compacton...

Physical Review Letters, 2016

Nonclassical states of the second optical harmonic in the presence of self-action

2Nd International Workshop on Squeezed States and Uncertainty Relations, Mar 1, 1993

Eprint Arxiv 0711 1808, Nov 1, 2007

We derive a cross-Kerr type effective Hamiltonian for the four-level atom interacting with three ... more We derive a cross-Kerr type effective Hamiltonian for the four-level atom interacting with three electromagnetic fields in the N-configuration. When the atom has relaxed into the ground state a cross-Kerr nonlinearity arises between two weak probe fields. As a development on earlier work we show in general that the atom will also display a linear and self-Kerr response. However, if certain resonance conditions are satisfied then the linear and self-Kerr interactions will vanish. The electrical susceptibilities of the probe transitions are also explored and it is shown that a large, pure cross-Kerr nonlinearity can be generated with vanishing absorption of both probe fields.

Physical Review a Atomic Molecular and Optical Physics, 2006

We formulate polarization uncertainty relations and polarization squeezing criteria in a SU͑2͒ in... more We formulate polarization uncertainty relations and polarization squeezing criteria in a SU͑2͒ invariant manner. In this formulation the SU͑2͒ coherent states are the only minimum uncertainty states. We show that polarization squeezing is a nonclassical property. We analyze the relation between polarization squeezing and other nonclassical properties such as entanglement and quadrature squeezing.

Weak values and entanglement concentration

AIP Conference Proceedings, 2009

Weak values and entanglement concentration. [AIP Conference Proceedings 1110, 9 (2009)]. David Me... more Weak values and entanglement concentration. [AIP Conference Proceedings 1110, 9 (2009)]. David Menzies, Natalia Korolkova. Abstract. Weak measurements are a special class of indirect measurements where the signal system ...

Physical Review Letters, 2015

A beam splitter is a basic linear optical element appearing in many optics experiments and is fre... more A beam splitter is a basic linear optical element appearing in many optics experiments and is frequently used as a continuous-variable entangler transforming a pair of input modes from a separable Gaussian state into an entangled state. However, a beam splitter is a passive operation that can create entanglement from Gaussian states only under certain conditions. One such condition is that the input light is suitably squeezed. We demonstrate experimentally that a beam splitter can create entanglement even from modes which do not possess such a squeezing provided that they are correlated to but not entangled with a third mode. Specifically, we show that a beam splitter can create three-mode entanglement by acting on two modes of a three-mode fully separable Gaussian state without entangling the two modes themselves. This beam splitter property is a key mechanism behind the performance of the protocol for entanglement distribution by separable states. Moreover, the property also finds application in collaborative quantum dense coding in which decoding of transmitted information is assisted by interference with a mode of the collaborating party.

26 Quantum Structure of Fiber Solitons and Quantum Communication

Amplitude squeezing in asymmetric fiber Sagnac interferometer operating on two polarizations

m with a pulse width around 130 fs. The nonlinear Kerr effect dominates the propagation owing to ... more m with a pulse width around 130 fs. The nonlinear Kerr effect dominates the propagation owing to the high peak power of up to 3.5kW. A half wave plate aligns the linearly po- larized light coming from the laser at a 45 angle with respect to the two main axes of the fiber ensuring an equal energy distribution between them.

Direct experimental text of non-separability and other quantum techniques using continuous variables of light

We present schemes for the generation and evaluation of continuous variable entanglement of brigh... more We present schemes for the generation and evaluation of continuous variable entanglement of bright optical beams and give a brief overview of a variety of optical techniques and quantum communi- cation applications on this basis. A new entanglement-based quantum interferometry scheme with bright beams is suggested. The performance of the presented schemes is independent of the relative interference phase which