Quantum logic operations are the elemental operations for quantum computing and have been implemented in various time-evolved atomic systems. Here, we present a scheme to simulatively implement the typical quantum NOT- and Hadamard gates operations, alternatively with the coupled three-waveguide structure (rather than the usual atomic levels); two modes in sinuous waveguides encoding the two logic states of a qubit and the mode in the center straight waveguide serve as auxiliary the coupler. Based on the Lewis-Riesenfeld invariant theory, we show that the desired mode conversions for implementing the NOT gate and mode split to realize the Hadamard gate are fast achieved by engineering the coupling parameters between the optical waveguides. The implementations of the logic gates demonstrated here relay on the structure parameters of the waveguides, rather than the durations of time evolutions with the usual driven atomic systems, and thus should be feasible robustly with the current integrated optical technology.
Quantum logic operations are the elemental operations for quantum computing and have been implemented in various time-evolved atomic systems. Here, we present a scheme to simulatively implement the typical quantum NOT- and Hadamard gates operations, alternatively with the coupled three-waveguide structure (rather than the usual atomic levels); two modes in sinuous waveguides encoding the two logic states of a qubit and the mode in the center straight waveguide serve as auxiliary the coupler. Based on the Lewis-Riesenfeld invariant theory, we show that the desired mode conversions for implementing the NOT gate and mode split to realize the Hadamard gate are fast achieved by engineering the coupling parameters between the optical waveguides. The implementations of the logic gates demonstrated here relay on the structure parameters of the waveguides, rather than the durations of time evolutions with the usual driven atomic systems, and thus should be feasible robustly with the current integrated optical technology.
Trapped-ion qubits promise certain fundamental advantages for quantum information processing (QIP), owing to their indistinguishability and relatively high isolation from noisy environments. Though these qualities have allowed demonstrations of the necessary primitives for quantum computation, the complexity of the optical apparatus required is a major impediment to implementation at scales where quantum systems offer a clear advantage over classical computers. Here, we build on previous work with trap-integrated waveguide optics, describing designs and simulations for commercial foundry-fabricated ion trap chips with integrated Si3N4 waveguides and grating couplers to implement multi-qubit operations. We detail a design intended to address and implement quantum logic gates between 5 ions in a single register, and a configuration which utilizes the stable on-chip path lengths of waveguide devices to enact a novel fast entangling two-qubit gate. The devices and approaches presented here could form elements of a scalable architecture for trapped-ion QIP.
Quantum logic gates are basic blocks to construct quantum computing and quantum information processing systems.
Quantum logic gates based on coupled-resonator optical waveguide (CROW) are analyzed with the advantage of integration
with other devices. Photonic crystal CROW (PhC CROW) structure with different dimension and background medium
exhibits electromagnetically induced transparency (EIT), which is used as single quantum bit (qubit) phase gate. Quantum
Hadamard gate can also be realized by coupling element. Two qubit conditional quantum phase gate is achieved by
concatenating two Hadamard gates and a phase gate doped with dopant. The simplicity and dynamic tunability of the device…
Unlike classical digital computers in which a bit can represent either 1 or 0 at any time, quantum computers use a two-level system, i.e., a qubit, to implement logical operations based on quantum mechanical laws, which can represent both values at once. Owing to the superposition property of qubits, quantum computers have natural parallel processing advantages and thus have potential to exceed the computational efficiency of classical computers for particular tasks. Quantum logic gates are the generalization of classical logic gates in computational networks. It has been proved that two-qubit quantum gates together with one-qubit quantum gates are adequate for constructing networks with any possible quantum computational property. Directional couplers are the most critical elementsfor constructing the quantum gates. In recent years, photonic quantum technologies have emerged as a promising experimental platform for quantum computing. Single photons have robust noise resistance, long coherence time, high transmission speed and great compatibility with other systems. They can be easily manipulated and encoded in any of several degrees of freedom, for example, polarization, path, spatial mode or time bin. Optical waveguide technology enables the realizing of complex optical schemes comprised of many elements with desired scalability, stability and miniaturization. Femtosecond laser direct writing of waveguide has been adopted as a powerful tool for integrated quantum photonics with characteristics of rapidness, cost-effectiveness, mask-less and single-step process. In particular, it has the ability to build arbitrary three-dimensional circuits directly inside bulk materials, which is impossible to achieve with conventional lithography. In this article we review the femtosecond laser writing and quantum characterization of directional coupler and important one-qubit and two-qubit optical quantum logic gates, such as Hadamard gate, Pauli-X gate, controlled-NOT gate, and controlled-Phase gate. The qubits in these gates are usually encoded through optical paths or polarizations of photons. The key to the realization of polarization-encoded one-qubit gates is to achieve flexible wave-plate operations, which is described in detail. Controlled-NOT gate and controlled-phase gate are the most crucial two-qubit gates in the linear optics computation and sometimes they can be converted into each other by adding some one-qubit gates or special superposition states. Many different kinds of waveguide circuits have been used to implement these two-qubit gates. The outlook and challenges for the femtosecond laser writing of three-qubit gates, such as Toffoli gate and Fredkin gate, are briefly introduced.
Abstract In quantum optical computing both of Pauli X, Y, Z gates and Hadamard gate are essential and important issues. Several proposals are given for addressing these issues. In this paper, the authors propose polarization encoded all-optical schemes which implement Hadamard logic, Pauli X, Pauli Y and Pauli Z gates followed by Hadamard logic gate separately. An integrated scheme is also proposed where three Pauli gates (X, Y and Z) followed by a single Hadamard gate is developed using polarization encoding mechanism. The outputs of the proposed systems follow the truth tables of the respective operations exactly. As the systems use the polarization character of light, so fully quantum optical operations with superfast speed are achieved.
We solve the Jaynes-Cummings Hamiltonian with time-dependent coupling parameters under the dipole and rotating-wave approximations for a three-dimensional photonic crystal (PC) single-mode cavity with a sufficiently high-quality Q factor. We then exploit the results to show how to create a maximally entangled state of two atoms and how to implement several quantum logic gates: a dual-rail Hadamard gate, a dual-rail NOT gate, and a SWAP gate. The atoms in all of these operations are syncronized, which is not the case in previous studies of PCs [J. Mod. Opt.48, 1495 (2001); Eur. Phys. J. D10, 285 (2000); Eur. Phys. J. D18, 247 (2002)]. Our method has the potential for extension to N-atom entanglement, universal quantum logic operations, and the implementation of other useful, cavity QED-based quantum information processing tasks.
Abstract The system of two coupled optical dual-mode waveguides is considered. The coupling of the system is studied to find a circuit for building a control switch for two qubit gates. The classical coupled mode theory is applied and the exact expressions for coupling coefficients are derived. The parameters of the system for performing the desired operations are numerically computed and analysed. The system describing the influence of intermodal interactions is solved numerically. The distortions are analysed.