Abstract
Silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals due to the relatively long spin coherence times. For these spin qubits, donor electron charge manipulation by external gates is a key ingredient for control and read-out of single-qubit operations, while shallow donor exchange gates are frequently invoked to perform two-qubit operations. More recently, charge qubits based on tunnel coupling in P+2 substitutional molecular ions in Si have also been proposed. We discuss the feasibility of the building blocks involved in shallow donor quantum computation in silicon, taking into account the peculiarities of silicon electronic structure, in particular the six degenerate states at the conduction band edge. We show that quantum interference among these states does not significantly affect operations involving a single donor, but leads to fast oscillations in electron exchange coupling and on tunnel-coupling strength when the donor pair relative position is changed on a lattice-parameter scale. These studies illustrate the considerable potential as well as the tremendous challenges posed by donor spin and charge as candidates for qubits in silicon.
Highlights
Most of the computer-based encryption algorithms presently in use to protect systems accessible to the public, in particular over the Internet, rely on the fact that factoring a large number into its prime factors is so computationally intensive that it is practically impossible
The exponential speedup of Shor’s algorithm is due to the intrinsic quantum parallelism in the superposition principle and the unitary evolution of quantum mechanics. It implies that a computer made up of entirely quantum mechanical parts, whose evolution is governed by quantum mechanics, would be able to carry out in reasonably short time prime factorization of large numbers that is prohibitively time-consuming in classical computation, revolutionizing cryptography and information theory
The feasibility of charge qubits based on P+2 molecular ions in Si is investigated in Sec. 5, where we focus on the tunnel coupling and charge coherence in terms of electron-phonon coupling
Summary
Most of the computer-based encryption algorithms presently in use to protect systems accessible to the public, in particular over the Internet, rely on the fact that factoring a large number into its prime factors is so computationally intensive that it is practically impossible. As transistors and integrated circuits decrease in size, the physical properties of the devices are becoming sensitive to the actual configuration of impurities (Voyles et al 2002) In this context, the first proposal of donor-based silicon QC by Kane (Kane 1998), in which the nuclear spins of the monovalent 31P impurities in Si are the qubits, has naturally created considerable interest in revisiting all aspects of the donor impurity problem in silicon, in the Si:31P system. The first proposal of donor-based silicon QC by Kane (Kane 1998), in which the nuclear spins of the monovalent 31P impurities in Si are the qubits, has naturally created considerable interest in revisiting all aspects of the donor impurity problem in silicon, in the Si:31P system In principle, both spin and electronic orbital degrees of freedom can be used as qubits in semiconductor nanostructures. The feasibility of charge qubits based on P+2 molecular ions in Si is investigated in Sec. 5, where we focus on the tunnel coupling and charge coherence in terms of electron-phonon coupling
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