We study two squeezed-state-dependent schemes of the quantum optical tap for information encoded in quantum-correlated fields from a two-mode entangled source. We find that, by using two independent squeezed beam splitters, the quantum information encoded in entangled dual beams can be divided into four parts without noise increase. We calculate the corresponding transfer coefficients to confirm that quantum optical tapping is achieved. As a variation to the original tapping schemes, we consider parametric amplifiers to replace beam splitters as tapping devices and find that they work equally well and have the advantage of tolerance to external losses. We also analyze the scalability of the schemes by cascading two outputs into the next stage and find that the output signals of the first stage can be further split noiselessly by the second stage. This shows that the scheme is cascadable and scalable for efficient quantum information distribution in an optical network.
We study two squeezed-state-dependent schemes of the quantum optical tap for information encoded in quantum-correlated fields from a two-mode entangled source. We find that, by using two independent squeezed beam splitters, the quantum information encoded in entangled dual beams can be divided into four parts without noise increase. We calculate the corresponding transfer coefficients to confirm that quantum optical tapping is achieved. As a variation to the original tapping schemes, we consider parametric amplifiers to replace beam splitters as tapping devices and find that they work equally well and have the advantage of tolerance to external losses. We also analyze the scalability of the schemes by cascading two outputs into the next stage and find that the output signals of the first stage can be further split noiselessly by the second stage. This shows that the scheme is cascadable and scalable for efficient quantum information distribution in an optical network.
We demonstrate that a phase-insensitive parametric amplifier, when coupled to a quantum correlated source, can be used as a quantum information tap for noiseless three-way signal splitting. We find that the output signals are amplified noiselessly in two of the three output ports, while the other can more or less keep its original input size without adding noise. This scheme can be cascaded and scaled up for efficient information distribution in an optical network. Furthermore, we find that this scheme satisfies the criteria for a nonideal quantum nondemolition (QND) measurement and thus can serve as a QND measurement device. With two readouts correlated to the input, we find this scheme also satisfies the criterion for a sequential QND measurement.
One of the important functions in a communication network is the distribution of information. It is not a problem to accomplish this in a classical system since classical information can be copied at will. However, challenges arise in quantum system because extra quantum noise is often added when the information content of a quantum state is distributed to various users. Here, we experimentally demonstrate a quantum information tap by using a fiber optical parametric amplifier (FOPA) with correlated inputs, whose noise is reduced by the destructive quantum interference through quantum entanglement between the signal and the idler input fields. By measuring the noise figure of the FOPA and comparing with a regular FOPA, we observe an improvement of 0.7 ± 0.1 dB and 0.84 ± 0.09 dB from the signal and idler outputs, respectively. When the low noise FOPA functions as an information splitter, the device has a total information transfer coefficient of Ts+Ti = 1.5 ± 0.2, which is greater than the classical limit of 1. Moreover, this fiber based device works at the 1550 nm telecom band, so it is compatible with the current fiber-optical network for quantum information distribution.
Abstract We propose a method to generate an entangled squeezed state using an optical parametric amplifier (OPA) and a beam splitter (BS). This device can manipulate the output quantum light field by modulating two parameters: the intensity of the OPA and the transmittance of the optical BS. For the output quantum state associated with a symmetric BS, there is no quadrature squeezing. Moreover, neither photon correlation nor entanglement are observed. However, in terms of sum squeezing, the quantum state corresponding to the symmetric BS is the strongest. Therefore, an asymmetric BS and a highly squeezing OPA are the best choices for generating the quantum entangled squeezed states.
Abstract Multiphoton catalysis is a non-Gaussian operation which has aroused interest recently in quantum information processing. There are two schemes of multiphoton catalysis in the current literature: one uses a beam splitter, while the other uses an optical parametric amplifier. We derive the catalysis operator in the Fock basis for each scheme and find a close relationship between them. We propose to enhance quantum entanglement of the two-mode squeezed vacuum state by performing two-mode multiphoton catalysis independently using two beam splitters. We calculate the optimal entanglement, which is maximized over two independent transmissivities, for the catalyzed states with various pairs of catalysis photon numbers, and find that in each case entanglement is enhanced only when the squeezing parameter is below a certain threshold. We also find that the optimal entanglement is nonzero in the limit of low squeezing, and deduce the analytical forms of the limiting catalyzed state and its entanglement in each case from numerical coefficients.
Quantum entanglement is a resource in quantum metrology that can be distributed to two conjugate physical quantities for the enhancement of their measurement sensitivity. This is demonstrated in the joint measurement of phase and amplitude modulation signals in quantum dense metrology schemes. We can also devote all the quantum resource to phase measurement only, leading to the optimum sensitivity enhancement. In this paper, we experimentally implement a dual-beam sensing scheme in an SU(1,1) interferometer for the optimum quantum enhancement of phase measurement sensitivity. We demonstrate a 3.9-dB improvement in signal-to-noise ratio over the optimum classical method, and this is 3-dB better than the traditional single-beam scheme. Furthermore, such as cheme also realizes a quantum optical tap of quantum entangled fields and has the full advantages of an SU(1,1) interferometer, such as detection loss tolerance, making it more suitable for practical applications in quantum metrology and quantum information.
We investigate the deterministic generation and distribution of entanglement in large quantum networks by driving distant qubits with the output fields of a nondegenerate parametric amplifier. In this setting, the amplifier produces a continuous Gaussian two-mode squeezed state, which acts as a quantum-correlated reservoir for the qubits and relaxes them into a highly entangled steady state. Here we are interested in the maximal amount of entanglement and the optimal entanglement generation rates that can be achieved with this scheme under realistic conditions taking, in particular, the finite amplifier bandwidth, waveguide losses, and propagation delays into account. By combining exact numerical simulations of the full network with approximate analytic results, we predict the optimal working point for the amplifier and the corresponding qubit-qubit entanglement under various conditions. Our findings show that this passive conversion of Gaussian into discrete-variable entanglement offers a robust and experimentally very attractive approach for operating large optical, microwave, or hybrid quantum networks, for which efficient parametric amplifiers are currently developed.