Nonlocal Gate Research Articles

Optimizing local protocols for implementing bipartite nonlocal unitary gates using prior entanglement and classical communication

We present a method of optimizing recently designed protocols for implementing an arbitrary nonlocal unitary gate acting on a bipartite system. These protocols use only local operations and classical communication with the assistance of entanglement, and are deterministic while also being "one-shot", in that they use only one copy of an entangled resource state. The optimization is in the sense of minimizing the amount of entanglement used, and it is often the case that less entanglement is needed than with an alternative protocol using two-way teleportation.

Universal quantum gates between distant quantum dot spins

We propose a scheme to engineer a nonlocal two-qubit phase gate between two remote quantum-dot spins in cavities. As the effect of cavity decay is considered and strong coupling condition is not used, the scheme has good adaptability. Along with single qubit operations, one can perform in principle various types of distributed quantum information processing.

Distributed quantum information processing via quantum dot spins

We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing.

IMPLEMENTATION OF NON-LOCAL TOFFOLI GATE VIA CAVITY QUANTUM ELECTRODYNAMICS

A scheme for realizing the non-local Toffoli gate among three spatially separated nodes through cavity quantum electrodynamics (C-QED) is presented. The scheme can obtain high fidelity in the current C-QED system. With entangled qubits as quantum channels, the operation is resistive to actual environment noise.

Efficient implementation of a nonlocal gate with nonmaximal entanglement

We present two schemes for efficient implementation of a nonlocal gate with nonmaximal entanglement. The main strategy of the schemes is local conversion of pure states, which consists of a generalized measurement described by a positive operator-valued measure (POVM), one-way classical communication, and corresponding unitary operations. First, we discuss the way to generate determinately the nonlocal gate via any pure shared entangled state combined with entanglement-assistance. Then we propose the other way to generate probabilistically the nonlocal gate via any pure entangled state with the aid of ancillary particles.

Remote unambiguous discrimination of linearly independent symmetric d-level quantum states

A set of linearly independent nonorthogonal symmetric d-level quantum states can be discriminated remotely and unambiguously with the aid of two-level Einstein–Podolsky–Rosen (EPR) states. We present a scheme for such a kind of remote unambiguous quantum state discrimination (UD). The probability of discrimination is in agreement with the optimal probability for local unambiguous discrimination among d symmetric states (Chefles and Barnettt 1998 Phys. Lett. A 250 223). This scheme consists of a remote generalized measurement described by a positive operator valued measurement (POVM). This remote POVM can be realized by performing a nonlocal 2d × 2d unitary operation on two spatially separated systems, one is the qudit which is encoded by one of the d symmetric nonorthogonal states to be distinguished and the other is an ancillary qubit, and a conventional local von Neumann orthogonal measurement on the ancilla. By decomposing the evolution process from the initial state to the final state, we construct a quantum network for realizing the remote POVM with a set of two-level nonlocal controlled-rotation gates, and thus provide a feasible physical means to realize the remote UD. A two-level nonlocal controlled-rotation gate can be implemented by using a two-level EPR pair in addition to local operations and classical communications (LOCCs).

Controlled implementation of a nonlocal and open-target destination quantum controlled-Not （CNOT） gate using partially entangled pairs

We show how a nonlocal and open-target destination quantum controlled-Not （CNOT） gate can be probabilistically implemented by using partially entangled pairs of particles. We first investigate the controlled implementation of a nonlocal and three-target destination CNOT gate using three partially entangled pairs, and then generalize the scheme to the case of N-target destination. In this scheme, Alice’s local generalized measurement described by a positive operator valued measurement （POVM） plays a key role. We construct the required POVM. It is worth noting that deterministic and exact implementation of a nonlocal CNOT gate can be realized using partially entangled pairs.

Implementation of Nonlocal Controlled-NOT Gate via a Cavity Input-Output Process

Quantum entanglement, which is a novel feature distinguishing quantum mechanics from classical physics, has been widely used in quantum information processing [1{7] and quantum computing [8,9]. In recent years, people have paid much attention to the quantum logic gate and have devoted themselves to the implementation of the quantum logic gate with di erent physical systems, such as cavity quantum electrodynamics (QED) [10], linear optics [11], ion trap [12], nuclear magnetic resonance (NMR) [13], etc. It is well known that quantum information can be encoded in the states of atom, ion and photon. However, compared with the atom and the ion, the photon has some special advantages; for example, it weakly interacts with the environment and the operational convenience of single-qubit and two-qubit logic gates in linear optical ways can be realized. All these features make the photon more appropriate as an ideal carrier for quantum information and more appropriate for use as ying qubits that interact with stationary qubits (atom or ion). Recently, Duan and Kimble proposed a scheme to implement a two-photon quantum controlled phase ip (CPF) gate via a cavity input-output process [14]. In

Electron Substrate and Gate Current Modeling for Single-Drain Buried-Channel p-Type Metal–Oxide–Semiconductor Field-Effect Transistors Including Tunneling Mechanisms

A model of nonlocal electron substrate and gate currents is presented for single-drain (SD) buried-channel (BC) p-type metal–oxide–semiconductor field-effect transistors (pMOSFETs). A nonlocal impact ionization coefficient with characteristic length dependence both in the exponential term and the pre-exponential factor is used in the electron substrate current model. The gate current model is developed by originating a modified lucky electron concept that includes quantum-mechanical tunneling effects in parallel. The channel electric field is first calculated by using an analytical pseudo-two-dimensional MOSFET model, and the spatial distribution of electron temperature along the channel is then derived using a simplified energy balance equation. Having calculated the nonlocal impact ionization coefficient and electron temperature, and modified the lucky electron concept, the nonlocal electron substrate and gate currents can be derived. This model is a time-saving computer-aided-design (CAD) model and is physics transparent for SD BC pMOSFETs.

Robust Implementation of a Nonlocal N-Qubit Phase Gate by Interference of Polarized Photons

We propose a protocol to directly implement the nonlocal phase gate of N A-type three-level atoms trapped in distant cavities by using interference of polarized photons. The protocol uses the effects of quantum statistics of indistinguishable photons emitted by the atoms inside optical cavities.

Implementation of Non-local Operations for High-Dimensional SystemsThrough Qubit Quantum Channels

We propose a method to implement akind of non-local operation betweenspatially separated two systems with high dimensions by using only alow-dimensional qubit quantum channel and 2-bit classical communication. Forqutrit systems, we further show the creation of non-local maximallyentangled state and the construction of the non-local quantum XOR gate interms of the obtained non-local operations as well as some single qutritlocal gates.

A new protocol for constructing nonlocal n-qubit controlled-U gates

We present a new protocol for constructing a nonlocal n-qubit controlled-U gate. In this protocol, no prior sharing of entanglement is needed and only one ancilla qubit is sent once from one party to another. Thus, the present protocol is very efficient for performing a nonlocal multiqubit controlled-U gate, which is important to network quantum information processing and communication.

Nonlocal gate of quantum network via cavity quantum electrodynamics

We propose an experimentally feasible scheme to realize the nonlocal gate between two different quantum network nodes. With an entanglement-qubit (ebit) acts as a quantum channel, our scheme is resistive to actual environment noise and can get high fidelity in current cavity quantum electrodynamics (C-QED) system.

Probabilistic implementation of a nonlocal operation using a nonmaximally entangled state

We develop the probabilistic implementation of a nonlocal gate $\exp{[i\xi{\sigma_{n_A}}\sigma_{n_B}]}$ and $\xi\in[0,\frac\pi4]$, by using a single non-maximally entangled state. We prove that, nonlocal gates can be implemented with a fidelity greater than 79.3% and a consumption of less than 0.969 ebits and 2 classical bits, when $\xi\leq0.353$. This provides a higher bound for the feasible operation compared to the former techniques \cite{Cirac,Groisman,Bennett-1}. Besides, gates with $\xi\geq0.353$ can be implemented with the probability 79.3% and a consumption of 0.969 ebits, which is the same efficiency as the distillation-based protocol \cite{Groisman,Bennett-1}, while our method saves extra classical resource. Gates with $\xi\to0$ can be implemented with nearly unit probability and a small entanglement. We also generalize some application to the multiple system, where we find it is possible to implement certain nonlocal gates between many non-entangled partners using a non-maximally multiple entangled state.

Interaction cost of nonlocal gates.

We introduce the interaction cost of a nonlocal gate as the minimal time of interaction required to perform the gate when assisting the process with fast local unitaries. This cost, of interest both in the areas of quantum control and quantum information, depends on the specific interaction, and allows one to compare in an operationally meaningful manner any two nonlocal gates. In the case of a two-qubit system, an analytical expression for the interaction cost of any unitary operation given any coupling Hamiltonian is obtained. One gate may be more time consuming than another for any possible interaction. This defines a partial order structure in the set of nonlocal gates, that compares their degree of nonlocality. We analytically characterize this partial order in a region of the set of two-qubit gates.

A physics-based electron gate current model for fully depleted SOI MOSFETs

In this paper, we present a physics-based gate current model for submicron n-type fully depleted SOI MOSFETs. The gate current model is developed by using the conventional lucky-electron concept and quantum-mechanical tunneling mechanism, and the effect of self-heating of SOI device is included. First, the channel electric field is calculated, and then the electron temperature is generated; the electron temperature is derived using a simplified energy balance equation. From the electron temperature, we can calculate the non-local gate current. This model is a time-saving CAD model and many interesting and important device physics about gate current can be found. The accuracy of the presented model has been verified with the experimental data of SOI devices.

A MOSFET gate current model with the direct tunneling mechanism

In this paper, we report a model for calculating the gate current as a function of gate and drain biases by considering the quantum-mechanical effect. Using a WKB approximation for the transmission probability, direct and Fowler–Nordheim tunneling currents across thin gate oxides of MOSFETs have been modeled for carriers from the inversion layers in Si substrate. The modeled direct tunneling currents have been compared to experimental data obtained from MOSFETs with oxide thickness of 2 nm. The gate current model is developed by using a pseudo-2D and analytical drain current model as a basis to generate channel electric field and electron temperature, which is derived using a simplified energy balance equation. From the electron temperature, we can calculate the non-local gate current. This model is a time-saving CAD model.

A non-local gate current and oxide trapping charge generation model for lightly doped drain and single-drain nMOSFETs

In this paper, we present a non-local gate current model for sub-micron lightly doped drain (LDD) and single-drain (SD) MOSFETs. Using this model and a trapping charge mechanism, we can calculate the spatial oxide trapping charge due to the electron transport in the oxide. This model is developed by using a modified lucky electron concept to include the quantum-mechanical tunneling effect. The channel electric field is first calculated by using an analytical pseudo-2-D MOSFET model, the spatial distribution of electron temperature is generated, and the electron temperature is then derived by using a simplified energy balance equation. From the electron temperature, we calculate the spatial gate current density, and using a first-order charge trapping mechanism, we finally calculate the distribution of non-local oxide trapping charge. This model is a time-saving CAD model and is physics transparent.