Quantum CNOT Gate Research Articles

Implementation of a polarization-encoded quantum CNOT gate

Abstract Optics has been successfully used for data processing. The basic building blocks of quantum computers are the quantum gates. Here, a quantum CNOT gate is proposed. To implement the gate advantages of polarization-based encoding technique and optical Kerr material-based switching are utilized. CS2 can show this type of switching feature. An Nd-YAG laser source of 1.064 μm wavelength is used to implement the scheme. Intensity of the laser pulse should be of the order of 1018 W/m2 to excite the 2nd order nonlinearity of the isotropic nonlinear material.

Work and heat in quantum CNOT gate operations

Work and heat in quantum CNOT gate operations

Realization of the quantum CNOT gate based on multiphoton process in multimode Cavity QED

We propose a scheme for implementing the CNOT gate in which the photonic qubits encoded on the cavity modes and a four-level atom passes through the cavity. The location of the resonance is predicted from the use of effective three-level Hamiltonian. First, we have theoretically studied the interaction of multi-level atom with multi-mode fields in a cavity by using the shore’s method. Next we have numerically calculated the probability of the state of the interest as well as the fidelity of this scheme. We have also used the wave-function and the density matrix approaches to study theoretically and numerically the effects of decoherence in the implementation of the gate.

Controlled alternate quantum walk-based pseudo-random number generator and its application to quantum color image encryption

Pseudo-random number generator (PRNG) are a key component in the design of modern cryptographic mechanisms and are regarded as a backbone element of many modern cryptographic applications. However and in spite of their robustness, quantum computers could crack down PNGR-based systems. Quantum walks, a universal model of quantum computation, have nonlinear properties that make them a robust candidate to produce PRNG. In this paper, we utilize controlled alternate quantum walk (CAQW) to create PRNG. Moreover, we use the presented PRNG mechanism as a component of a new quantum color image encryption protocol. The quantum color image is encrypted via quantum C-Not (controlled-Not) gate which ruled by the key sequence generated from the PRNG mechanism. Simulation results and numerical analyses demonstrate that the suggested PRNG mechanism and its application to quantum color image encryption have high efficiency with high security.

A Quantum-Controlled NOT Gate Based on Four-Wave Mixing in a Cavity for Polarization Photonic Qubits

The possibility of effectively creating quantum gates based on polarization photon qubits using a Kerr nonlinear medium in a cavity is studied. It is shown how a quantum C-NOT gate can be produced with such qubits through four-wave mixing. A theory of this gate’s operation is constructed using an input–output formalism, and conditions of parametric matching are obtained for effective gate operation.

Control not quantum gate on the states of photon orbital angular momentum

The possibility of effectively creating quantum gates based on orbital angular momentum photon qubits using a Kerr nonlinear medium in a cavity is studied. It is shown how a quantum C-NOT gate can be produced with such qubits through four-wave mixing process. A theory of this gate operation is constructed using an input–output formalism. Parametric matching conditions are obtained for effective gate operation.

Hyperparallel optical quantum computation assisted by atomic ensembles embedded in double-sided optical cavities

We propose an effective, scalable, hyperparallel photonic quantum computation scheme in which photonic qubits are hyperencoded both in the spatial degrees of freedom (DOF) and the polarization DOF of each photon. The deterministic hyper-controlled-not (hyper-cnot) gate on a two-photon system is attainable with our interesting interface between the polarized photon and the collective spin wave (magnon) of an atomic ensemble embedded in a double-sided optical cavity, and it doubles the operations in the conventional quantum cnot gate. Moreover, we present a compact hyper-cnot${}^{N}$ gate on $N+1$ hyperencoded photons with only two auxiliary cavity-magnon systems, not more, and it can be faithfully constituted with current experimental techniques. Our proposal enables various applications with the hyperencoded photons in quantum computing and quantum networks.

Success Probability of Optical Quantum CNOT Gate Based on Probabilistic Single Photon Sources

Success Probability of Optical Quantum CNOT Gate Based on Probabilistic Single Photon Sources

Teleportation of a controlled-NOT gate for photon and electron-spin qubits assisted by the nitrogen-vacancy center

Teleportations of quantum gates are very important in the construction of quantum network and teleportation-based model of quantum computation. Assisted with nitrogenvacancy centers, we propose several schemes to teleport the quantum CNOT gate. Deterministic CNOT gate may be implemented on a remote two-photon system, remote two electron-spin system, hybrid photon-spin system or hybrid spin-photon system. Each photon only interacts with one spin each time. Moreover, quantum channel may be constructed by all combinations of the photon or electron-spin entanglement, or their hybrid entanglement. Since these electron-spin systems have experimentally shown a long coherence time even at the room temperature, our schemes provide useful ways for long-distance quantum applications.

Robust quantum gates via a photon triggering electromagnetically induced transparency

We propose a scheme to achieve a parallelized controlled-NOT (c-not) gate based on electromagnetically induced transparency (EIT) and cavity-assisted photon scattering. By using the flying photon as the control bit, we can implement a conditional transfer between two logical states of an atom trapped in the cavity with high fidelity and on a microsecond time scale. Thanks to the fact that the photon is well suited for scalable quantum computation, a quantum c-not gate between the single-photon pulses and the nonlocal gate on remote atoms are obtained by reflecting the photon pulse from an optical cavity with a single-trapped atom. Our protocol is robust for spontaneous emission and works quite well in the bad-cavity limit, which makes it more applicable in the laboratory with current experimental techniques.

All Optical Quantum CNOT Gate in Semiconductor Quantum Dots

Using density matrix approach the possibility of quantum logic operation in a single semiconductor quantum dot (QD) has been explored. The two photon excitation of the QD creates population in the biexciton state which is subsequently depopulated by the second pulse resonant with the biexciton-exciton transition. The theoretical analysis suggest that CNOT gate can be formed by choosing the pulses of appropriate pulse area.

Physical Realization of Quantum C-Not Gate

We investigate a Heisenberg spin cluster with two particles controlled by a time-dependent magnetic field. The system is controlled by tuning the amplitude, frequency, and interaction time of the three-step time-dependent magnetic field. Then we solve the time-dependent Schrödinger equation of the two-particle system, and obtain the time evolution operator. By the three-timestep interaction, the wavefunction evolves from the initial state to the final state, and the total evolution operator can be expressed as a product of the three evolution operators. By adjusting the physical parameters, the key two-qubit logic gate, the C-Not gate, can be realized physically.

Simulations of quantum gates with decoherence

Methods and results for numerical simulations of one and two interacting rf-SQUID systems suitable for adiabatic quantum gates are presented. These are based on high accuracy numerical solutions to the static and time dependent Schr\"odinger equation for the full SQUID Hamiltonian in one and two variables. Among the points examined in the static analysis is the range of validity of the effective two-state or ``spin-$\frac{1}{2}$'' picture. A range of parameters is determined where the picture holds to good accuracy as the energy levels undergo gate manipulations. Some general points are presented concerning the relations between device parameters and ``good'' quantum mechanical state spaces. The time dependent simulations allow the examination of suitable conditions for adiabatic behavior, and permits the introduction of a random noise to simulate the effects of decoherence. A formula is derived and tested relating the random noise to the decoherence rate. Sensitivity to device and operating parameters for the logical gates NOT and CNOT are examined, with particular attention to values of the tunnel parameter $\ensuremath{\beta}$ slightly above one. It appears that with values of $\ensuremath{\beta}$ close to 1, a quantum CNOT gate is possible even with rather short decoherence times. Many of the methods and results will apply to coupled double-potential well systems in general.

Adiabatic evolution of a coupled-qubit Hamiltonian

We present a general method for studying coupled qubits driven by adiabatically changing external parameters. Extended calculations are provided for a two-bit Hamiltonian whose eigenstates can be used as logical states for a quantum CNOT gate. From a numerical analysis of the stationary Schroedinger equation we find a set of parameters suitable for representing CNOT, while from a time-dependent study the conditions for adiabatic evolution are determined. Specializing to a concrete physical system involving SQUIDs, we determine reasonable parameters for experimental purposes. The dissipation for SQUIDs is discussed by fitting experimental data. The low dissipation obtained supports the idea that adiabatic operations could be performed on a time scale shorter than the decoherence time.

Design of adiabatic logic for a quantum CNOT gate

We examine the realization of a quantum CNOT gate by adiabatic operations. The principles of such systems and their analysis are briefly discussed and a model consisting of two weakly coupled double-potential well qubits is studied numerically. Regions of the parameter space with suitable well-defined sets of wavefunctions are found, in which then an adiabatic sweep of an external bias produces the switching behavior of CNOT. Results are presented on the adiabatic condition and the identification with the parameters of a flux-coupled two-SQUID system is given. For typical parameters adiabatic times in the nanosecond regime are obtained.