Symmetric informationally complete positive operator-valued measures provide efficient quantum state tomography in any finite dimension. In this work, we implement using symmetric for both pure and mixed photonic qudit states Hilbert spaces of orbital angular momentum, including whose dimension is not power a prime. Fidelities reconstruction within the range 0.81–0.96 are obtained states. These results relevant to high-dimensional information computation experiments, especially those where...

We experimentally demonstrate a new measurement scheme for the discrimination of two coherent states. The is based on displacement operation followed by photon-number-resolving detector, and we show that it outperforms standard homodyne detector which we, in addition, prove to be optimal within all Gaussian operations including conditional dynamics. also non-Gaussian superior continuous variable quantum key distribution scheme.

We demonstrate for the first time feasibility of free space quantum key distribution with continuous variables under real atmospheric conditions. More specifically, we transmit coherent polarization states over a 100 m channel on roof our institute's building. In scheme, signal and local oscillator (LO) are combined in single spatial mode, which auto-compensates fluctuations results an excellent interference. Furthermore, LO acts as spectral filter, thus allowing unrestrained daylight operation.

We investigate quantum measurement strategies capable of discriminating two coherent states probabilistically with significantly smaller error probabilities than can be obtained using nonprobabilistic state discrimination. apply a postselection strategy to the data homodyne detector as well photon number resolving in order lower probability. compare different receivers an optimal intermediate scheme where rate is minimized for fixed inconclusive results. The (PNR) receiver experimentally...

A generalization of the Bell states and Pauli matrices to dimensions which are powers 2 is considered. basis maximally entangled multidimensional bipartite (MEMBS) chosen very similar standard constructed only symmetric antisymmetric states. This special MEMBS preserves all basic properties We present a recursive non-recursive method for construction discuss their properties. The possess property rotationally invariant exclusive correlations rotational invariance singlet state.

We present a protocol for quantum key distribution using discrete modulation of coherent states light. Information is encoded in the variable phase which can be chosen from regular set ranging binary to continuous modulation, similar phase-shift-keying classical communication. decoded by simultaneous homodyne measurement both quadratures and requires no active choice basis. The utilizes either direct or reverse reconciliation, with without postselection. analyze security show how enhance it...

In this paper, a DC arc discharge plasma with copper vapour admixtures is studied by synchronized laser absorption (LAS) and optical emission spectroscopy (OES). The spatial spectral characteristics of the between electrodes in an argon flow at atmospheric pressure were analysed. spectra recorded OES methods excitation temperatures population energy levels atom corresponding to upper transitions wavelengths work determined. turn, LAS method was used determine lower level one under study....

We address the long-standing problem of discriminating coherent states with minimum error rate. show an optimum receiver for which admits a relatively simple implementation current technologies. The is based on multichannel splitting signal, followed by feed-forward signal displacement and photon-counting detection. develop optimal control strategy finite split convergence rate to Helstrom bound.

We propose a method to produce pure single photons with an arbitrary designed temporal shape in heralded, lossless and scalable way. As the indispensable resource, uses pairs of time-energy entangled photons. To accomplish shaping, one photon pair undergoes modulation according desired shape. Subsequent frequency-resolving detection heralds its counterpart quantum state non-locally affected by modulation. found conditions for heralded reproduce function. The can be implemented various...

We experimentally demonstrate a quantum receiver based on Kennedy scheme for discrimination between two phase-modulated weak coherent states. The is assembled entirely from the standard fiber-optic elements and operates at conventional telecom wavelength 1.55 microns. local oscillator signal are transmitted through different optical fibers, displaced measured with high-efficiency superconducting nanowire single-photon detector. show error rate times below shot-noise limit.

We investigate the properties of an atmospheric channel for free space quantum communication with continuous polarization variables. In our prepare-and-measure setup, coherent states are transmitted through 100m length on roof institute's building. The signal measured by homodyne detection help a local oscillator (LO) which propagates in same spatial mode as signal, orthogonally polarized to it. Thus interference and LO is excellent fluctuations autocompensated. also acts spectral filter,...

We propose a method for quantum noise extraction from the interference of laser pulses with random phase. Our technique is based on calculation parameter, which we called reduction factor, and allows determination contributions classical noises assumption that fluctuations exhibit Gaussian distribution. To best our knowledge, concept factor introduced first time. use such an approach to implement post-processing-free optical number generator bit generation rate 2 Gbps.

Gain-switched lasers are in demand numerous quantum applications, particularly, systems of key distribution and various optical random number generators. The reason for this popularity is natural phase randomization between gain-switched laser pulses. idea such has become so familiar that most authors use it without regard to the features operation mode they use. However, at high repetition rates pulses or when generated a bias current close threshold, condition may be violated. This paper...

We justify that homodyne tomography turns out to be informationally complete when the number of independent quadrature measurements is equal dimension density matrix in Fock representation. Using this as our thread, we examine completeness other schemes continuous-variable observations are truncated discrete finite-dimensional subspaces.

We study the generation of single-photon pulses with tailored temporal shape via nonlocal spectral filtering. A shaped photon is heralded from a time-energy entangled pair upon filtering and time-resolved detection its counterpart. show that defined by time-inverted impulse response filter does not depend on heralding instant. Thus one can avoid postselection particular instants achieve substantially higher rate photons as compared to modulation. Furthermore, method be used generate...

Single-pixel imaging (SPI) is an alternative method for obtaining images using a single photodetector, which has numerous advantages over the traditional matrix-based approach. However, most experimental SPI realizations provide relatively low resolution compared to systems. Here, we show simple yet effective scale up of SPI. Our system utilizes patterns based on Hadamard matrices, which, when reshaped variable aspect ratio, allow us improve along one axes, while sweeping improves second...

We employ a straightforward relation between mutually unbiased and Bell bases to extend the latter in terms of direct construction for former. analyze detail properties these generalized states, showing that they constitute an appropriate tool testing entanglement bipartite multiqudit systems.

High sensitivity imaging at the level of single photons is an invaluable tool in many areas, ranging from microscopy to astronomy. However, development single-photon sensitive detectors with high spatial resolution very non-trivial. Here we employ single-pixel approach and demonstrate a proof-of-principle setup. We overcome problem low light gathering efficiency by developing large-area microstrip superconducting photon detector coupled multi-mode optical fiber interface. show that setup...

We put forward a generic method that enables lossless generation of pure single photons with arbitrary shape over any degree freedom or several degrees simultaneously. The exploits pairs entangled photons. One the is subject for lossy shaping manipulations followed by specially designed mode-equalizing measurement. A successful measurement outcome heralds losslessly shaped second photon. has three crucial ingredients define quantum state photon: initial bipartite photons, modulation first...

Passive side-channel attacks in quantum key distribution (QKD) aim at obtaining information about the signals without disturbing them and hence compromise real-world QKD security. Currently, there are no reliable tools for assessment of signal generation imperfections. In this work we propose a generic experimental method which allows to upper-bound light-source imperfections directly integrate into modern security proofs. The relies on Hong-Ou-Mandel interference between different emitted...

A quantum-information analysis of how the size and dimensionality quantum alphabet affect critical error rate quantum-key-distribution (QKD) protocols is given on an example two QKD protocols---the six-state \ensuremath{\infty}-state (i.e., a protocol with continuous alphabet) ones. In case two-dimensional Hilbert space, it shown that, under certain assumptions, increasing number letters in up to infinity slightly increases rate. Increasing additionally space leads further increase

We report on a continuous variable analogue of the triplet two-qubit Bell states. discuss symmetry properties entangled states either kind, and theoretically experimentally demonstrate remarkable similarity two-mode with respect to their correlation patterns. Understanding helps finding decoherence-free subspaces.