Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.
The development of quantum annealing machines (QAMs) based on superconducting qubits has progressed greatly in recent years and these machines are now widely used in both academia and commerce. On the other hand, QAMs based on semiconductor nanostructures such as quantum dots (QDs) appear to be still at the initial elementary research stage because of difficulty in controlling the interaction between qubits. In this paper, we review a QAM based on a semiconductor nanostructures such as floating gates (FGs) or QDs from the viewpoint of the integration of qubits. We theoretically propose the use…
We theoretically show that spontaneously interlayer-coherent bilayer quantum Hall droplets should allow robust and fault-tolerant pseudospin quantum computation in semiconductor nanostructures with voltage-tuned external gates providing qubit control and a quantum Ising Hamiltonian providing qubit entanglement. Using a spin-boson model we estimate decoherence to be small $(\sim 10^{-5})$.
Shor's factoring algorithm illustrates the potential power of quantum computation. Here we present and numerically investigate a proposal for a compiled version of such an algorithm based on a quantum-wire network exploiting the potentialities of fully coherent electron transport assisted by the surface acoustic waves. Specifically, a non standard approach is used to implement, in a simple form, the quantum circuits of the modular exponentiation execution for the simplest instance of the Shor's algorithm, that is the factorization of $N$=15. The numerical procedure is based on a time-dependent…
We study the zitterbewegung of electronic wave packets in III-V zinc-blende semiconductor quantum wells due to spin-orbit coupling. Our results suggest a direct experimental proof of this fundamental effect, confirming a long-standing theoretical prediction. For electron motion in a harmonic quantum wire, we numerically and analytically find a resonance condition maximizing the zitterbewegung.
Device concepts in semiconductor spintronics make long spin lifetimes desirable, and the requirements put on spin control by schemes of quantum information processing are even more demanding. Unfortunately, due to spin-orbit coupling electron spins in semiconductors are generically subject to rather fast decoherence. In two-dimensional quantum wells made of zinc-blende semiconductors, however, the spin-orbit interaction can be engineered in such a way that persistent spin structures with extraordinarily long spin lifetimes arise even in the presence of disorder and imperfections. We review exp…
We demonstrate storage of excitons in a single nanostructure, a self-assembled Quantum Post. After generation electron and holes forming the exciton are separated by an electric field towards opposite ends of the Quantum Post inhibiting their radiative recombination. After a defined time such spatially indirect excitons are reconverted to optically active direct excitons by switching the electric field. The emitted light of the stored exciton is detected in the limit of a single nanostructure and storage times exceeding 30 msec are demonstrated. We identify a slow tunneling of the electron out…
A major question for condensed matter physics is whether a solid-state quantum computer can ever be built. Here we discuss two different schemes for quantum information processing using semiconductor nanostructures. First, we show how optically driven coupled quantum dots can be used to prepare maximally entangled Bell and Greenberger-Horne-Zeilinger states by varying the strength and duration of selective light pulses. The setup allows us to perform an all-optical generation of the quantum teleportation of an excitonic state in an array of coupled quantum dots. Second, we give a proposal for …
Theoretical prediction of phonon transport in modern semiconductor nanodevices requires atomic resolution of device features and quantum transport models covering coherent and incoherent effects. The nonequilibrium Green's function method (NEGF) is known to serve this purpose very well, but is numerically very expensive. This work extends the very efficient Büttiker probe concept to phonon NEGF and discusses all implications of this method. Büttiker probe parameters are presented that reproduce within NEGF experimental phonon conductances of Si and Ge between 10K and 1000K. Results of this met…
Focusing and guiding light into semiconductor nanostructures can deliver revolutionary concepts for photonic devices, which offer a practical pathway towards next-generation power-efficient optical networks. In this review, we consider the prospects for photonic switches using semiconductor quantum dots (QDs) and photonic cavities which possess unique properties based on their low dimensionality. The optical nonlinearity of such photonic switches is theoretically analyzed by introducing the concept of a field enhancement factor. This approach reveals drastic improvement in both power-density a…
We calculate the exchange coupling J between electrons in a double-well potential in a two-dimensional semiconductor environment within the Heitler-London (HL) approach. Two functional forms are considered for the double-well potential. We show that by choosing an appropriate and relatively simple single-electron variational wave function it is possible, within the HL approach, to significantly improve the estimates for J. In all cases the present scheme overcomes the artifacts and limitations at short interdot distances, previously attributed to the HL method, where unphysical triplet ground …
Microscopic approach to the quantized light-matter interaction in semiconductor nanostructures: Complex coupled dynamics of excitons, biexcitons, and photons
The exchange coupling of the spins of two electrons in double well potentials in a semiconductor background is calculated within the Heitler-London (HL) approximation. Atomic and quantum dot types of confining potentials are considered, and a systematic analysis for the source of inaccuracies in the HL approach is presented. For the strongly confining coulombic atomic potentials in the H2 molecule, the most dramatic failure occurs at very large interatomic distances, where HL predicts a triplet ground state, both in 3D and in 2D, coming from the absence of electron-electron correlation effects…
The long dreamed quantum internet would consist of a network of quantum nodes (solid-state or atomic systems) linked by flying qubits, naturally based on photons, travelling over long distances at the speed of light, with negligible decoherence. A key component is a light source, able to provide single or entangled photon pairs. Among the different platforms, semiconductor quantum dots are very attractive, as they can be integrated with other photonic and electronic components in miniaturized chips. In the early 1990s two approaches were developed to synthetize self-assembled epitaxial semicon…
We propose an implementation scheme for holonomic, i.e., geometrical, quantum information processing based on semiconductor nanostructures. Our quantum hardware consists of coupled semiconductor macroatoms addressed/controlled by ultrafast multicolor laser-pulse sequences. More specifically, logical qubits are encoded in excitonic states with different spin polarizations and manipulated by adiabatic time-control of the laser amplitudes . The two-qubit gate is realized in a geometric fashion by exploiting dipole-dipole coupling between excitons in neighboring quantum dots.
Recently, de Visser and Blaauboer [Phys. Rev. Lett. {\bf 96}, 246801 (2006)] proposed the most efficient deterministic teleportation protocol $\cal T$ for electron spins in a semiconductor nanostructure consisting of a single and a double quantum dot. However, it is as yet unknown if $\cal T$ can be completed before decoherence sets in. In this paper we analyze the detrimental effect of nuclear spin baths, the main source of decoherence, on $\cal T$. We show that nonclassical teleportation fidelity can be achieved with $\cal T$ provided certain conditions are met. Our study indicates that real…
We theoretically consider solid state nuclear spins in a semiconductor nanostructure environment as long-lived, high-fidelity quantum memory. In particular, we calculate, in the limit of a strong applied magnetic field, the fidelity versus time of P donor nuclear spins in random bath environments of Si and GaAs, and the lifetime of excited intrinsic spins in polarized Si and GaAs environments. In the former situation, the nuclear spin dephases due to spectral diffusion induced by the dipolar interaction among nuclei in the bath. We calculate the decay of nuclear spin quantum memory in the cont…
Semiconductor quantum dots integrated with ultrafast spectroscopy technology are prime candidates for building scalable architectures for Quantum Information Processing. In this review paper we survey the current state of theoretical proposals concerning all-optical control of nanostructure qubits and their interactions. These schemes offer potential for ultrafast optical manipulation of quantum information in time scales within the coherence time.
This paper reviews both experimental and theoretical work on nanostructures showing high quantum yields due to the phenomenon of multiple exciton generation. It outlines the aims and barriers to progress in identifying further such nanostructures, and also includes developments concerning solar devices where nanostructures act as the light-absorbing component. It reports on both semiconductor and carbon structures, both monocomposite (of various dimensionalities) and heterogeneous. Finally, it looks at future directions that can be taken to push solar cell efficiency above the classic limit se…
Novel qubits in hybrid semiconductor-superconductor nanostructures
Delft University of Technology（代尔夫特理工大学）；IBM Research Europe（IBM欧洲研究院）；Consejo Superior de Investigaciones Científicas (CSIC)（西班牙高等科学研究委员会）；Instituto de Ciencia de Materiales de Madrid (ICMM)（马德里材料科学研究所）；Institute of Science and Technology Austria（奥地利科学技术研究所）；New York University（纽约大学）
We propose an implementation of holonomic (geometrical) quantum gates by means of semiconductor nanostructures. Our quantum hardware consists of semiconductor macroatoms driven by sequences of ultrafast laser pulses ({\it all optical control}). Our logical bits are Coulomb-correlated electron-hole pairs (excitons) in a four-level scheme selectively addressed by laser pulses with different polarization. A universal set of single and two-qubit gates is generated by adiabatic change of the Rabi frequencies of the lasers and by exploiting the dipole coupling between excitons.
We propose a solid-state implementation of stimulated Raman adiabatic passage in two coupled semiconductor quantum dots. Proper combination of two pulsed laser fields allows the coherent carrier transfer between the two nanostructures without suffering significant losses due to environment coupling. By use of a general solution scheme for the carrier states in the double-dot structure, we identify the pertinent dot and laser parameters.
