We present an improved phase estimation scheme employing entangled coherent states and demon- strate that the give smallest variance in parameter comparison to NOON, BAT "optimal" under perfect lossy conditions. As these advantages emerge for very modest particle numbers, optical version of state metrology is achievable with current technology.

We show that nonlinear problems including partial differential equations can be efficiently solved by variational quantum computing. achieve this utilizing multiple copies of states to treat nonlinearities and introducing tensor networks as a programming paradigm. The key concepts the algorithm are demonstrated for Schr\"{o}dinger equation canonical example. numerically ansatz exponentially more efficient than matrix product present experimental proof-of-principle results obtained on an IBM Q device.

We investigate two schemes of quantum teleportation with a W state, which belongs to different class from the Greenberger–Horne–Zeilinger class. In first scheme, state is shared by three parties, one whom, called sender, performs Bell measurement. It shown that information an unknown split between parties and recovered certain probability. second sender takes particles positive operator valued measurements. For schemes, we calculate success probability average fidelity. show fidelity scheme...

We investigate the phase enhancement of quantum states subject to nonlinear shifts. The optimal estimation even entangled coherent (ECSs) is shown be better than that NOON with same average particle number $\ensuremath{\langle}n\ensuremath{\rangle}$ and nonlinearity exponent $k$. creation an approximate state (AECS) from a photon-subtracted squeezed vacuum current optical technology methods show pure AECS ECS for large $\ensuremath{\langle}n\ensuremath{\rangle}$. Finally, we examine simple,...

We propose a hybrid quantum algorithm based on the Harrow-Hassidim-Lloyd (HHL) for solving system of linear equations. In our scheme, classical information feed-forward is required from phase estimation to reduce circuit depth original HHL algorithm. this paper, we show that functionally identical under assumption number qubits used in algorithms large enough. addition, it experimentally examined with four IBM Quantum Experience setups, and experimental results higher accurate performance...

We show that electromagnetically-induced transparency and lasing without inversion are simultaneously achieved for microwave fields by using a fluxonium superconducting circuit. As result of the $\Delta$ energy-level structure this artificial three-level atom, we find surprising phenomenon window in frequency domain is sandwiched between absorption on one side amplification other side.

Optimization of the fidelity control operations is critical importance in pursuit fault-tolerant quantum computation. We apply optimal techniques to demonstrate that a single drive via cavity circuit electrodynamics can implement high-fidelity two-qubit all-microwave gate directly entangles qubits mutual qubit-cavity couplings. This performed by driving at one qubits' frequencies which generates conditional gate, but will also generate other spurious interactions. These are used find pulse...

Entangled coherent states are shown to emerge, with high fidelity, when mixing and squeezed vacuum of light on a beam-splitter.These maximally entangled states, where photons bunch at the exit beam-splitter, measured experimentally by Fock-state projections.Entanglement is examined theoretically using Bell-type nonlocality test compared ideal states.We show nearly perfect similarity for an optimal ratio light.In our scheme, generated deterministically small amplitudes, which could be...

We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The is two-level system and the bipartite quantum channel microwave photonic coherent between two cavities. A Bell-type measurement performed on hybrid of solid transfers discrete-variable electronic to cat cavity mode. In order facilitate implementation such complex protocols we design reducing self-Kerr nonlinearity cavity. teleporation enables...

We propose a scheme of loss-resilient entanglement swapping between two distant parties via an imperfect optical channel. In this scheme, copies hybrid entangled states are prepared and the continuous-variable parts propagate through lossy media. order to perform successful swapping, several different measurement schemes considered for such as single-photon detection ideal cases homodyne practical cases. find that using with small amplitudes offers larger than discrete-variable in presence...

We define an entanglement measure, called the partial tangle, which represents residual two-qubit of a three-qubit pure state. By its explicit calculations for states, we show that tangle is closely related to faithfulness teleportation scheme over

In this paper, we consider teleportation capability, distillability, and nonlocality on three-qubit states. order to investigate some relations among them, first find the explicit formulas of quantities about maximal fidelity We show that if any state is useful for then distillable into a Greenberger-Horne-Zeilinger state, violates specific form Mermin inequality teleportation.

We suggest and investigate a scheme for non-deterministic noiseless linear amplification of coherent states using successive photon addition, (â(†))(2), where â(†) is the creation operator. compare it with previous proposal addition-then-subtraction, ââ(†), â annihilation operator, that works as an appropriate amplifier only weak light fields. show when amplitude state |α| ≳ 0.91, (â(†))(2) operation serves more efficient compared to ââ(†) in terms equivalent input noise. Using basic...

Optical lattices with one atom on each site and interacting via cold controlled collisions provide an efficient way to entangle a large number of qubits high fidelity. It has already been demonstrated experimentally that this approach is especially suited for the generation cluster states [O. Mandel et al., Nature 425, 937 (2003)] which reduce resource requirement quantum computing ability perform single-qubit rotations qubit read out. In paper, we describe how implement these in...

We consider the possibility of performing linear optical quantum computation making use extra photonic degrees freedom. In particular we focus on case where photons as quadbits. The basic 2-quadbit cluster state is a hyper-entangled across polarization and two spatial mode examine non-deterministic methods whereby such states can be created from single and/or Bell pairs, then give some mechanisms for higher-dimensional fusion gates.

The engineering of Kerr interactions has great potential for quantum information processing applications in multipartite systems and investigation many-body physics a complex cavity-qubit network. We study how coupling multiple different types superconducting qubits to the same cavity modes can be used modify self- cross-Kerr effects acting on cavities demonstrate that this type architecture could significant benefit technologies. Using both analytical perturbation theory results numerical...

We propose a scheme for building heralded two-qutrit entangled state from polarized photons. An optical circuit is presented to build the maximally two Bell pairs and ideal threshold detectors. Several schemes are discussed constructing pairs. also show how one can produce an unbalanced that could be of general purpose use in some protocols. In terms applications qutrit state, we mainly focus on demonstrate violation Collins–Gisin–Linden–Massar–Popescu inequality under restriction...

Abstract We propose a new scheme of measurement-based quantum computation (MBQC) using an error-correcting code against photon-loss in circuit electrodynamics. describe specific protocol logical single-qubit gates given by sequential cavity measurements for MBQC and generalised Schrödinger cat state is used continuous-variable (CV) qubit captured microwave cavity. To apply on the qubit, we utilise d -dimensional system called qudit. It assumed that three CV-qudit entangled initially prepared...

Abstract Quantum backflow is a counterintuitive effect in which the probability density of free particle moves direction opposite to particle’s momentum. If electrically charged, then can be viewed as contrast between electric current and that To date, there has been no direct experimental observation quantum backflow. However, simulated numerically (using classical computers) optically light). In this study, we present first simulation using real computer.

Abstract Recent progress in quantum simulation and algorithms has demonstrated a rapid expansion capabilities. The search continues for new techniques applications to exploit advantage. Here we propose an innovative method investigate directly the properties of time-dependent density operator <?CDATA $\hat{\rho} (t)$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mi>ρ</mml:mi> <mml:mo stretchy="false">ˆ</mml:mo> </mml:mover>...

A W state is pair-wisely entangled, belonging to the different class from Greenberger, Horne, and Zeilinger (GHZ) state. We show that enables three variant protocols, is, quantum key distribution between several parts, secret sharing, both of them at same time. It discussed how one's cheating can be detected in each protocol.