Quantum computer hardware based on rare-earth-ion-doped inorganic crystals

We present a scheme for generating multiple, strongly interacting qubits in rare-earth-ion-doped inorganic crystals at cryogenic temperatures. Two ground state hyperfine levels, with hour long lifetimes and ms decoherence times are chosen as qubit states. Controlled logic between the qubits is accomplished using the change in permanent dipole moment induced by an optical transition between the ground and excited state of these ions. The scheme is based on existing material data and established measurement techniques and should therefore be straightforward to realise in practice. The procedure used for creating the qubits can be generalised also to other solid state systems.     

Quantum structure of solids

This paper reviews the interrelations between experiment and theory as they relate to the microscopic understanding of the material properties of solids. Three topics are emphasized: Pseudopotentials, fundamental optical spectra, and covalent bonding. The latter approach, although usually regarded as chemical and qualitative, has been made physical and quantitative in crystals by combining results of the first two approaches.     

Photon echoes in an amplifying rare-earth-ion-doped crystal

We report what we believe is the first experimental demonstration of photon echoes in an amplifying rare-earth-ion-doped crystal. Population inversion is achieved by optical pumping, which yields high-power photon echoes, with an energy gain of as much as a factor of 5. Effects of the pump on the photon echo process highlight the advantages of an amplifying crystal. New questions concerning the optical dephasing mechanisms in Er3+:YSO have arisen.     

Quantum diffusion of muon and muonium in solids

The quantum tunneling diffusion of muon and muonium in crystalline solids is discussed with emphasis on the effects of disorder and superconductivity. The complex effect of disorder on muonium diffusion in inhomogeneous crystals is scrutinized. The enhanced muon diffusion in the superconducting state of high-purity tantalum establishes the predominant influence of conduction electrons on the quantum diffusion in metals.     

Laser-induced damage and light scattering in solids

The article deals with the present-day status of the problem of damage to transparent solid dielectrics such as crystals, glasses, and others. The role of the absorbing inclusions and of self-focusing in the laser damage mechanism is discussed, as are also the limiting mechanisms connected with the electron avalanche.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 101, pp. 3–8, 1978.     

Quantum dynamics of electric-dipole coupled defect centers in solids

We investigate the quantum dynamics of two defect centers in solids,which are coupled by vacuum-induced dipole-dipole interactions.When the interaction between defects and phonons is taken into account,the two coupled electron-phonon systems make up two equivalent multilevel atoms.By making Born-Markov and rotating wave approximations,we derive a master equation describing the dynamics of the coupled multilevel atoms.The results indicate the concepts of subradiant and superradiant states can be applied to these systems and the population transfer process presents different behaviors from those of the two dipolar-coupled two-level atoms due to the participation of phonons.     

Quantum fluctuations in second-harmonic light generation

Second-harmonic light generation (SHLG) is analyzed from the viewpoint of the photon statistics of the fundamental and generated beams versus the path traversed by the two waves in the medium. The calculations lead to an anti-bunching effect for coherent incident light.     

Phase-coupling-induced ultraslow light propagation in solids at room temperature

We show that the group velocities of light pulses can be decelerated dramatically by the use of a dispersive phase-coupling effect through a wave mixing process. We have observed experimentally such a phase-coupling-induced ultraslow light propagation with a group velocity as low as 0.05 m/s in a photorefractive Bi12SiO20 crystal at room temperature. Moreover, the ultraslow light is amplified in the Bi12SiO20 crystal because of the unidirectional energy transfer from a coupling beam to the ultraslow light. This technique to produce ultraslow light propagation is valid for all nonlinear wave mixing processes with a dispersive phase-coupling effect.     

Quantum memory for squeezed light

We produce a 600-ns pulse of 1.86-dB squeezed vacuum at 795 nm in an optical parametric amplifier and store it in a rubidium vapor cell for 1 mus using electromagnetically induced transparency. The recovered pulse, analyzed using time-domain homodyne tomography, exhibits up to 0.21+/-0.04 dB of squeezing. We identify the factors leading to the degradation of squeezing and investigate the phase evolution of the atomic coherence during the storage interval.     

Quantum diffusion of light interstitials

The diffusion rate of light interstitials is calculated avoiding the usual adiabatic and Condon approximations for the phonons. The method employed is a generalization of the standard small polaron theory taking explicitely account of the strongly coupled interstitial-host vibrations.     

Quantum lithography with classical light

We show how to achieve subwavelength diffraction and imaging with classical light, previously thought to require quantum fields. By correlating wave vector and frequency in a narrow band, multiphoton detection process that uses Doppleron-type resonances, we show how to achieve arbitrary focal and image plane patterning with classical laser light at submultiples of the Rayleigh limit, with high efficiency, visibility, and spatial coherence. A frequency-selective measurement process thus allows one to simulate, semiclassically, the path-number correlations that distinguish a quantum entangled field.     

Quantum tunneling of light particles in metals

The motion of a particle in a metallic crystal is studied for low temperatures where transitions between adjacent interstitial sites are caused by quantum tunneling. The influence of electrons and phonons on the hopping rate is taken into account by means of a functional integral method. The electronic influence may effectively be described by Ohmic damping which dominates the low temperature behavior of the defect motion. When subsequent tunneling transitions are statistically independent, the diffusion constant is found to obey a power law, D∼T^2K−1, where K depends on the defect-electron interaction. This power law is limited at low temperatures by the effects of phonon excitations. Near the transition between electron and phonon dominated behavior the diffusion constant has a minimum where the precise temperature dependence of the rate depends not only on phonon spectra but also on the processes limiting phonon lifetimes.     

Quantum diffusion of light interstitials in metals

A quantum theory of diffusion of self-trapped light interstitials in metals is presented. The theory encompasses both coherent and incoherent tunneling, but the approximation used neglects the dependence of the interstitial transfer matrix element on the vibrational state of the crystal. The coherent tunneling contribution is estimated by fitting the incoherent diffusion rate to experimental data for hydrogen and muon diffusion. It is predicted that coherent diffusion should be dominant below ～ 80 K for H in Nb and below ～ 190 K for μ⁺ in Cu. Experimental verifications of these predictions would require high purity strain free samples and low concentrations of the diffusing species.     

Quantum tunnelling of vacancies in light metals

Summary The usefulness of the WKB method is illustrated by calculating characteristic tunnelling rates in several elemental solids and establishing the temperatures at which the tunnelling becomes of comparable importance to the thermally activated processes. In this way we have verified the importance of tunnelling which dominates the low-temperature region, while it becomes negligible above a temperature value depending on the mass and the barrier thickness. In studying vacancy migration in lithium metal we have considered various pathways in the configuration space of Li atoms. A (1, 1, 1)-jump of the vacancy, accompanied by the simultaneous outward movement of between 4 to 12 lithium atoms, is shown to be most efficient. In this model the lithium motion achieves a 10⁴-fold increase in the jump probability and a reduction of the activation energy from ∼0.25 to ∼0.16 eV.

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Riassunto L’utilità del metodo WKB è illustrata calcolando la probabilità di transizione per tunnelling in diversi solidi elementari e stabilendo la temperature alla quale il contributo del tunnelling diviene confrontabile con quello dovuto ai processi termicamente attivati. In tal modo si stabilisce l’importanza del tunnelling che domina la regione delle basse temperature, mentre divience trascurabile a temperature piú alte, dipendenti dalla massa e dallo spessore della barriera. Studiando il moto di vancaze nel litio, sono stati considerati diversi cammini nello spazio delle configurazioni degli atomi Li. Un salto della vacanza nella direzione (1, 1, 1), accompagnato dal simultaneo spostamento di 4÷12 atomi di litio, è dimostrato essere il piú efficiente. In questo modello la probabilità di moto delle vacanze aumenta di un fattore 10⁴ con una riduzione dell’energia di attivazione da ∼0.25 a ∼0.16 eV.

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Резюме Метод ВКБ применяется для вычисления характеристических вероятностей туннельных переходов в некоторых злементарных твердых телах. Определяются температуры, при которых туннелирование дает сравнимый вклад в термически активированные процессы. Мы показываем важность туннелирования, которое доминирует в области низких температур, но становится пренебрежимо малым при более высоких температурах, которые зависят от массы и толщины барьера. Исследуя движение вакансий в литии, мы рассматриваем различные траектории в конфигурационном пространстве атомов лития. Показывается, что скачок вакансии в направлении (1, 1, 1), который сопровождается одновременно смещением от 4 до 12 атомов лития, является наиболее эффективным. В этой модели вероятность движения вакансии увеличивается в 10⁴ раз при уменьшении энергии активации от ∼0.25 эВ до ∼0.16 эВ.