We demonstrate that, in a quantum computer with perpetually coupled qubits, all excitations can be confined to their sites (qubits) even without refocusing. The on-site localization is obtained b) ...
We demonstrate that, in a quantum computer with perpetually coupled qubits, all excitations can be confined to their sites (qubits) even without refocusing. The on-site localization is obtained by constructing a sequence of qubit energies that efficiently suppresses resonant hopping. The time during which a many-excitation state remains strongly localized in an infinite chain can exceed the reciprocal hopping frequency by $\agt 10^5$ already for a moderate bandwidth of qubit energies. The proposed energy sequence is also convenient for performing quantum operations on the qubits.
We demonstrate that, in a many-particle system, particles can be strongly confined to their sites. The localization is obtained by constructing a sequence of on-site energies that efficiently suppresses resonant hopping. The time during which a many-particle state remains strongly localized in an infinite chain can exceed the reciprocal hopping frequency by $\agt 10^6$ already for a narrow energy bandwidth. The results show viability of quantum computers with time-independent qubit coupling.
Strong many-particle localization is studied in a 1D array of perpetually coupled qubits and an equivalent 1D system of interacting fermions. We construct a bounded sequence of the on-site fermion energies, or qubit transition frequencies, that suppresses resonant hopping between both nearest and remote neighbors. Besides quasi-exponential decay of the single-particle transition amplitude,it leads to long lived strongly localized many-particle states. This makes quantum computing with time-independent qubit coupling viable.
We demonstrate the onset of strong on-site localization in a many-particle system, with effective localization length smaller than the intersite distance. The localization is obtained by constructing a bounded one-parameter sequence of on-site energies that eliminates resonant hopping between both nearest and remote sites. This sequence leads to quasiexponential decay of the single-particle transition amplitude. It also leads to on-site localization of stationary many-particle states in a finite-length chain. For an infinite many-particle system, we study the time during which all states remain on-site localized. We show that, for any number of particles, this time scales as a high power of the ratio of the bandwidth of on-site energies to the hopping integral. The proposed energy sequence is robust with respect to small errors. The formulation applies to fermions as well as perpetually coupled qubits. The results show viability of quantum computing with time-independent qubit coupling.
Many-particle confinement (localization) is studied for a 1D system of spinless fermions with nearest-neighbor hopping and interaction, or equivalently, for an anisotropic Heisenberg spin-1/2 chain. This system is frequently used to model quantum computers with perpetually coupled qubits. We construct a bounded sequence of site energies that leads to strong single-particle confinement of all states on individual sites. We show that this sequence also leads to a confinement of all many-particle states in an infinite system for a time that scales as a high power of the reciprocal hopping integral. The confinement is achieved for strong interaction between the particles while keeping the overall bandwidth of site energies comparatively small. The results show viability of quantum computing with time-independent qubit coupling.
We propose an approach to measuring coupled systems, which gives a parametrically smaller error than the conventional fast projective measurements. The measurement error is due to the excitations being not entirely localized on individual systems even where the excitation energies are different. Our approach combines spectral selectivity of the detector with temporal resolution and uses the ideas of the quantum diffusion theory. The results bear on quantum computing with perpetually coupled qubits.