Choice of the quantum probe state is of key importance to enhance the sensitivity of the Mach–Zehnder (MZ) interferometer beyond the classical one and even approach the quantum Cramér–Rao bound. According to the work of Caves (Caves 1981 Phys. Rev. D 23 1693), the quantum MZ interferometer is a phase-dependent one operating with single-mode squeezed vacuum (SMSV) light coupled with a coherent state. We use the SMSV state with squeezing <10 dB and report a gain in sensitivity of the phase-dependent MZ interferometer of more than 10 dB compared to the original result (Pezze and Smerzi 2008 Phys. Rev. Lett. 100 073601) via photon subtraction. The gain in sensitivity is also observed when measuring the difference in output intensities of the SMSV state with squeezing of < 3 dB from which two, four, and six photons are subtracted and a large coherent state. Overall, subtracting photons from the initially weakly squeezed light can prove to be a more efficient strategy in quantum MZ interferometry compared to highly squeezed SMSV state generation.

We review recent progress in the field of optical quantum metrology, with a focus on the analysis of the current level of theoretical and experimental research on the generation, transformation, and measurement of nonclassical states of light, such as NOON, squeezed, and hybrid states, which com- bine transformations of both discrete and continuous variables of a quantized light field. We show how such states can be used to improve the measurement accuracy and to estimate unknown phase parameters in both linear and nonlinear metrology. Sig- nificant attention is paid to the description of actual quantum metrology schemes that take the loss of particles, the limited fidelity of photon detectors, and other factors into account. We therefore identify both the ultimate (fundamental) bounds im- posed by quantum mechanical uncertainties of the quantities being measured and the bounds due to the effect of classical noise on the propagation and measurements of a quanti Of special importance are quantum metrology options spontaneous parametric light scattering, which, for m 50 years, has been an indispensable tool for key acc ments in quantum optics and related areas of photoni tum cryptography, quantum computing, and quantum In this regard, we analyze the current status of the u well-known Hong-Ou-Mandel photon anticorrelati and biphoton interference in various quantum metro proaches in measuring temperature, length, material co tion, and so on. We also discuss the use of biph photometry, radiometry, and sensing for the absolute tion of modern photon-count detectors, as well as for ments of the brightness temperature of hot radiation The quantum metrology phenomena, methods, aproaches discussed here in light of the most recent progress on sources and detectors of quantum radiation will be an important tool in developing and practically implementing new schemes and algorithms for quantum processing and information transmission.

Hybrid entangled states are necessary for quantum information processing within heterogeneous quantum networks. We develop an entanglement mechanism between continuous variable (CV) states of definite parity and delocalized photon (discrete variable (DV) state) leading to deterministic generation of the hybrid entangled states. The mechanism is realized by means of mixing of the input states on beam splitter (BS) with arbitrary transmission and reflection coefficients followed by measurement of the number of photons in the measurement mode by photon number resolving (PNR) detector. The scheme under study allows for one to partially control hybrid entanglement by change of the transmission/reflection coefficients of the BS. There are wide domains of values which guarantee the generation of maximum hybrid entanglement. The mechanism of the CV–DV entanglement can be used for controllable entangled state distribution in hybrid optical network.

Generation of the states with fidelity as close as possible to high-amplitude Schrödinger cat states (SCSs) is studied. The input state in the main mode is exclusively mixed with the Fock states on successive beam splitters after which a number of auxiliary modes emerge. Subsequently, all the modes are properly displaced. The resulting state is projected onto the vacuum states of every auxiliary mode for conditional generation of the target states in the main mode. We demonstrate a possibility to generate Schrödinger cat qudits (SCQs) which may approximate SCSs of large size β ranging from β = 2 to β = 3 with high fidelity close to 0.99 . The method is based on the use of the concept of SCQs being the best approximation of the SCSs in the finite Hilbert space with basic displaced number states characterized by the displacement amplitude α . Different states (e.g. number state or coherent state or superposed state) are selected as the input to the optical scheme. In particular, we show that an input Schrödinger kitten state (i.e. small-size SCS) can give rise to an output SCS of larger size. We also test the proposed approach in a realistic scenario.

We present a new method to entangle continuous variable (CV) states of certain parity and photonic states for the purpose of generating optical hybrid cluster (HC) states. To do it we introduce two families of the CV states of definite parity which stems from single mode squeezed vacuum (SMSV) state. Potential to apply the CV states of certain parity is high. We report on the generation of the even/odd Schrödinger cat state like (SCS-like) states whose fidelities with even/odd SCS of amplitude of 4.2 are more of 0.99 , when 30,31 photons are detected in auxiliary mode of input SMSV state initially mixed with single photon. We show that the quantum efficiency of a photon number resolving (PNR) detector is crucial to maintaining the success rate of even/odd SCSs generator at an acceptable level. The scheme with delocalized photon implements deterministic imperfect entanglement operation between macro and micro states. We show that the beam splitter implements the two-qubits operation control-Z (CZ) for input CV states of definite parity and photonic states, provided that certain result is detected in measurement mode. An extension of the entangling operation for two entangled delocalized photons (TEDP) allows one to realize three-qubit HC state. Seven-qubit HC state is the result of conjunction of two three-qubit HC states through TEDP state.

We theoretically propose an efficient way to generate optical analogs of both even and odd Schrӧdinger cat states (SCSs) of large amplitude with high fidelity and reasonable generation rate. The resources consumed are a single-mode squeezed vacuum state (SMSV) and possibly a single photon or nothing. We report the generation of even (odd) SCS with amplitude 4.2, fidelity higher than 0.99 with success probability a little more than 10−7 by subtraction of 30(31) photons from SMSV by ideal photon number detection. In order to reduce the requirements for the sensitivity of photon number resolving (PNR) detector, we show the implementation of even/odd SCSs with the same characteristics with two PNR detectors resolving only 15 photons each instead of 30. In the case of inefficient detector, SCS’s size and its fidelity can be kept close to perfect by using highly transmitting beam splitter, but at the cost of very dramatic reduction of the success probability. In order to have certain harmony between the characteristics (large amplitude, high fidelity and acceptable success probability) in the case of imperfect detection, highly transmitting beam splitters should not be used and number of the subtracted photons must be reduced to 1011.

We report an efficient way to generate both even and odd optical analogs of Schrodinger cat states (SCSs) which are a superposition of two coherent states with opposite amplitudes. The resources consumed are single mode squeezed vacuum (SMSV) state and single photon. SCSs are formed after superimposing the input states with the subsequent detection of the number of photons in the auxiliary mode. We report the generation of even/odd SCSs with amplitude 4.2 with fidelity >0.99 and an acceptable for offline experiments success probability. There is a tendency towards an increase in the size of the SCSs with the fidelity >0.99 more demonstrated with an increase in the number of extracted photons.

We propose an efficient way to generate optical analogs of both even and odd Schrodinger cat states (SCSs) with high fidelity, large amplitude and reasonable generation rate. The resource consumed are a single-mode squeezed vacuum state (SMSV) and possibly a single photon or nothing. We report the generation of even (odd) SCS with amplitude 4.2, fidelity higher than 0.99 and reasonable generation rate by subtraction of 30(31) photons from SMSV by ideal photon number detection. In the case of inefficient detectors, maintaining SCS size and its fidelity at the same level as in the case of ideal detectors results in a dramatic decrease in the success probability. In order to have certain harmony between the three characteristics (large amplitude, high fidelity and acceptable success probability for the generation scheme) in the case of imperfect detection, highly transmitting beam splitters should not be used and number of the subtracted photons must be reduced to 10(11).

We present novel theory of effective realization of large-size optical Schrödinger cat states, which play an important role for quantum communication and quantum computation in the optical domain using laser sources. The treatment is based on the α -representation in infinite Hilbert space which is the decomposition of an arbitrary quantum state in terms of displaced number states characterized by the displacement amplitude α . We find analytical form of the α -representation for both even and odd Schrödinger cat states which is essential for their generation schemes. Two schemes are proposed for generating even/odd Schrödinger cat states of large size | β | (| β | ≥ 2) with high fidelity F ( F ≈ 0.99). One scheme relies on an initially offline prepared two-mode entangled state with a fixed total photon number, while the other scheme uses separable photon Fock states as the input. In both schemes, generation of the desired states is heralded by the corresponding measurement outcomes. Conditions for obtaining states useful for quantum information processing are established and success probabilities for their generation are evaluated.

In this paper, the systematic method is developed to synthesize planar closed kinematic chains with all the possible kinds of multiple joints according to given K-independent loops and up to total multiple joint factor Vmax. First, the structural synthesis method of multiple joint kinematic chains based on the combination of corresponding simple and multiple joints is presented. Then, the complete atlas database containing all valid multiple joints in closed fractionated kinematic chains with up to 5 independent loops and up to 12 links is established and illustrated. Further, corresponding all possible 14 types of multiple joint assortments up to K = 5 and up to total multiple joint factor Vmax = 8 are obtained and classified in the tables for the first time. Next, the structural analysis of multiple-jointed fractionated kinematic chains with various total multiple joint factors is conducted, and main structural parameters are determinated. Finally, based on atlas database of synthesized kinematic chains with multiple joints, the examples of creation of robot manipulators are provided.

We present results of the analysis of several structural models of metallic and nonmetallic liquids. Models cover the region of expanded liquid phase and supercritical fluid phase. The goal is to show that there are at least two regions on phase diagram, where liquid phase has essentially different atomic structure. Dense liquid and loose liquid have different atomic and electronic properties, as it could be seen from experiments.

The Fisher-Widom (FW) line [1] separates the phase diagram into regions with different asymptotic behavior of the pair correlation function. The FW line can be obtained analytically if one gets exact expression for the pair correlation function, but it can not be done from experimental data, because the structure factor is measured for the limited range of wave vectors. We have found out that the approximate position of the FW line can be found from the local atomic arrangement in the Lennard-Jones model. We use this circumstance to analyse the structure of expanded liquid metals (Hg, Cs, Rb). The universal systems' behavior has been revealed, and it can be suggested that the FW line corresponds to the region where atomic and electronic properties change considerably.