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TWO-QBIT GATES BASED ON COUPLED QUANTUM WIRES

Susanna Reggiani, Andrea Bertoni, Paolo Bordone, ROSSELLA BRUNETTI, Carlo Jacoboni, MASSIMO RUDAN, Giorgio Baccarani

Published Jan 1, 2000• 0 citations
OpenAlex

Abstract

A solid-state implementation of a set of one- and two-qbit gates for quantum computing is proposed. The qbit is defined as the state of an electron running along two quantum wires, suitably coupled through a potential barrier with variable height and/or width. Single-qbit gates are implemented using the coupling between the two wires. The two-qbit gates have been designed using a Coulomb coupler to induce a mutual phase modulation of the two qbits. A number of runs have been performed using a time-dependent 2D Schrodinger solver.

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A solid-state implementation of a set of one- and two-qbit gates for quantum computing is proposed. The qbit is defined as the state of an electron running along two quantum wires, suitably coupled through a potential barrier with variable height and/or width. Single-qbit gates are implemented using the coupling between the two wires. The two-qbit gates have been designed using a Coulomb coupler to induce a mutual phase modulation of the two qbits. A number of runs have been performed using a time-dependent 2D Schrodinger solver.
A solid-state implementation of a set of one- and two-qbit gates for quantum computing is proposed. The qbit is defined as the state of an electron running along two quantum wires, suitably coupled through a potential barrier with variable height and/or width. Single-qbit gates are implemented using the coupling between the two wires. The two-qbit gates have been designed using a Coulomb coupler to induce a mutual phase modulation of the two qbits. A number of runs have been performed using a time-dependent 2D Schrodinger solver.
A solid-state implementation of a universal set of gates for quantum computation is proposed and analysed using a time-dependent 2D Schrödinger solver. The qubit is defined as the state of an electron propagating along a couple of quantum wires. The wires are suitably coupled through a potential barrier with variable height and/or width. It is shown how a proper design of the system allows the implementation of any one-qubit transformation. The two-qubit gate is realized through a Coulomb coupler able to entangle the quantum states of two electrons running in two wires of two different qubits. The simulated devices are GaAs—AlGaAs heterostructures that should be on the borderline of present semiconductor technology. An estimate of decoherence effects due to phonon scattering is also presented.
As the key requirement of a quantum computer is the creation and exploitation of entanglement, a detailed study of entangled states has been carried out with reference to a solid-state system based on coupled quantum wires. A brief review of the basic gates is given first, based on preliminary investigations, followed by the analysis of electrons running along coupled quantum wires. The particle dynamics has numerically been simulated by means of a time-dependent Schrodinger solver applied to a two-particle system. Results are reported showing entangled states created by means of suitable quantum-gate networks. Starting from these fundamental results, the complexity of some interesting circuits is addressed, showing both the application of the universal set of quantum gates to complex algorithms and the computational speedup achieved within the proposed implementation.
We propose a new solid state implementation of a quantum computer (quputer) using ballistic single electrons as flying qubits in 1D nanowires. We use a single electron pump (SEP) to prepare the initial state and a single electron transistor (SET) to measure the final state. Single qubit gates are implemented using quantum dots as phase shifters and electron waveguide couplers as beam splitters. A Coulomb coupler acts as a 2-qubit gate, using a mutual phase modulation effect. Since the electron phase coherence length in GaAs/AlGaAs heterostructures is of the order of 30μμμm, several gates (tens) can be implemented before the system decoheres.
Abstract We studied the dynamics of a pair of single-electron double quantum dots (DQDs) under longitudinal and transverse static magnetic fields and time-dependent harmonic modulation of their interaction couplings. We propose to modulate the tunnel coupling between the QDs to produce one-qubit gates and the exchange coupling between DQDs to generate entangling gates, the set of operations required for quantum computing. We developed analytical approximations to set the conditions to control the qubits and applied them to numerical calculations to test the accuracy and robustness of the analytical model. The results shows that the unitary evolution of the two-electron state performs the designed operations even under conditions shifted from the ideal ones.
We propose a method for implementing a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along the z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively. The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum-controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates using a box-shaped quantum dot model and numerically solving a time-dependent Schrödinger equation, and demonstrate that the quantum gates can perform quantum computations. The operating speed of the gates is about one operation per 4 ps. The reading operation of the output of the quantum computer can be performed by detecting the polarization of the qubits.