Back Cover: Nonreciprocal Unconventional Photon Blockade with Kerr Magnons (Adv. Quantum Technol. 8/2024)

Nonreciprocal photon-phonon entanglement in Kerr-modified spinning cavity magnomechanics

Difference‐Frequency Generation with and without Quantum Interference in Superconducting Circuits

AbstractElectromagnetically induced transparency (EIT) plays an important role in enhancing nonlinear optical processes at the quantum level. This paper proposes an accessible scheme for realizing high‐efficiency second‐order nonlinear difference‐frequency generation beyond the conventional EIT technique in superconducting circuits. By designing two subsystems to create two transparency windows from Autler–Townes splitting (ATS), a dual‐ATS mechanism is triggered in the scheme. This mechanism leads to an efficient difference‐frequency generation, and the efficiency obtained here can be four orders of magnitude larger than that of the EIT scheme. This study may pave a way for exploring ATS‐enhanced nonlinear optics.

Cavity Magnon-Polariton Interface for Strong Spin-Spin Coupling

Strong coupling between single qubits is crucial for quantum information science and quantum computation. However, it is still challenged, especially for single solid-state qubit. Here, we propose a hybrid quantum system, consisting of a coplanar waveguide (CPW) resonator weakly coupled to a single nitrogen-vacancy spin in diamond and a yttrium-iron-garnet (YIG) nanosphere holding Kerr magnons, to realize strong long-distance spin-spin coupling. With a strong driving field on magnons, the Kerr effect can squeeze magnons, and {thus the coupling between the CPW resonator and the sequeezed magnons is exponentially enhanced}, which produces two cavity-magnon polaritons, i.e., the high-frequency polariton (HP) and low-frequency polariton (LP). When the enhanced cavity-magnon coupling {approaches} the critical value (i.e., the frequency of the LP becomes zero), the spin is fully decoupled from the HP, while the coupling between the spin and the LP is significantly improved. In the dispersive regime, a strong spin-spin coupling mediated by the LP is achieved with accessible parameters. Our proposal indicates that the critical cavity-magnon polarition is a potential interface to realize strong spin-spin coupling and manipulates remote solid spins.

Nonreciprocal entanglement in cavity-magnon optomechanics

Optomechanical-interface-induced strong spin-magnon coupling

Strong single-photon optomechanical coupling in a hybrid quantum system

Engineering strong single-photon optomechanical couplings is crucial for optomechanical systems. Here, we propose a hybrid quantum system consisting of a nanobeam (phonons) coupled to a spin ensemble and a cavity (photons) to overcome it. Utilizing the critical property of the lower-branch polariton (LBP) formed by the ensemble-phonon interaction, the LBP-cavity coupling can be greatly enhanced by three orders magnitude of the original one, while the upper-branch polariton (UBP)-cavity coupling is fully suppressed. Our proposal breaks through the condition of the coupling strength less than the critical value in previous schemes using two harmonic oscillators. Also, strong Kerr effect can be induced in our proposal. This shows our proposed approach can be used to study quantum nonlinear and nonclassical effects in weakly coupled optomechanical systems.

Higher-order exceptional point in a pseudo-Hermitian cavity optomechanical system

Strong tunable spin-spin interaction in a weakly coupled nitrogen vacancy spin-cavity electromechanical system

Coherent perfect absorption in a weakly coupled atom-cavity system

Chaotic state as an output of vacuum state evolving in diffusion channel and generation of displaced chaotic state for quantum controlling

Quantum Zeno dynamics induced atomic entanglement in a hybrid atom-cavity-fiber system

Spin squeezing via one- and two-axis twisting induced by a single off-resonance stimulated Raman scattering in a cavity

Spectral features of the tunneling-induced transparency and the Autler-Townes doublet and triplet in a triple quantum dot

Tunable self-focusing and self-defocusing effects in a triple quantum dot via the tunnel-enhanced cross-Kerr nonlinearity

Amplification of the coupling strength in a hybrid quantum system

Cross-Kerr effect on an optomechanical system

Four-junction superconducting circuit

Magnon Kerr effect in a strongly coupled cavity-magnon system

Method for identifying electromagnetically induced transparency in a tunable circuit quantum electrodynamics system

Controllable coupling between a nanomechanical resonator and a coplanar-waveguide resonator via a superconducting flux qubit

ENTANGLEMENT CONCENTRATION WITH CROSS-KERR NONLINEARITY

We propose a protocol for realizing two entanglement concentration scheme with cross-Kerr nonlinearity and double cross-phase modulation method. In our protocols, two remote parties do not require the accurate information of the less entangled state and the double cross-phase modulation is introduced to overcome the errors caused by the imperfect Kerr interaction. By this way, a single-photon entanglement is concentrated, and a three-photon polarized GHZ state is also achieved. Furthermore this protocol can be scaled to multiphoton polarized GHZ state concentration and the giant Kerr media is not needed, which makes our protocols more feasible in experiment.

Generating the Schrödinger cat state in a nanomechanical resonator coupled to a charge qubit

Coupling spin ensembles via superconducting flux qubits

An Efficient Scheme for Entanglement Concentration of Arbitrary Four-Photon States

REALIZATION OF NONLOCAL QUANTUM GATE THROUGH ASSISTED-CAVITIES

We propose a scheme for implementing a three-qubit controlled-Not-Not (CNNOT) gate and a two-qubit SWAP gate between atoms and single-photon pulse through cavity QED. In the scheme, we can one-step realize multiple-qubit GHZ state and two-qubit Bell state by applying multiple-qubits CNNOT gate. We have also shown that our scheme would be robust against practical imperfections in current cavity QED experiment setup through simple numerical estimates. Finally, we provide the current parameters to show that our scheme is feasible.

Tunable optimal quantum cloning machines with trapped atoms

CONCENTRATING ARBITRARY FOUR-PHOTON LESS-ENTANGLED CLUSTER STATE BY SINGLE PHOTONS

We present a protocol for concentrating an arbitrary four-photon entangled state into a maximally entangled state assisted with singled photons. The concentration protocol uses the linear optics and the cross-Kerr nonlinearity based on the post selection principle. Four parties called Alice, Bob, Charlie and Dan in different distant locations can obtain the cluster state from an arbitrary entangled four-photon state with a certain probability. Quantum non-demolition (QND) measurements are available in this protocol. Moreover, this scheme can be steady with a higher success possibility.

SCHEME FOR GENERATION OF GREENBERGER-HORNE-ZEILINGER STATES OF REMOTE ATOMS TRAPPED IN SEPARATE OPTICAL CAVITIES

We propose a scheme for generating maximally entangled states for three atoms trapped in three distant cavities connected by two identical single-mode fibers. During the operation, neither the atomic system nor the fibers are excited, which is important in view of decoherence. Under certain conditions, the probability of the excited cavities can be negligible. Taking advantage of adiabatic passage, the GHZ state can be generated deterministically, and the fidelity of entanglement is insensitive to fluctuation of experimental parameters. Compared to the previous schemes, the significant advantage of the proposed scheme is that each cavity can interact with the other two directly, which can avoid the effect of indirect interaction brought about using only local quantum operator and nonlocal resources.

Optimal real state quantum cloning machine in cavity quantum electrodynamics

Schemes for entanglement concentration of two unknown partially entangled states with cross-Kerr nonlinearity

Scheme for generation of four-atom Greenberger–Horne–Zeilinger states in an optical cavity

Generation of Multiple-Atom Entangled States with Weak Cross-Kerr Nonlinearity

Implementing ancilla-free phase covariant quantum cloning with atoms trapped in cavities