Optical pumping and readout of bismuth hyperfine states in silicon for atomic clock applications

The push for a semiconductor-based quantum information technology has renewed interest in the spin states and optical transitions of shallow donors in silicon, including the donor bound exciton transitions in the near-infrared and the Rydberg, or hydrogenic, transitions in the mid-infrared. The deepest group V donor in silicon, bismuth, has a large zero-field ground state hyperfine splitting, comparable to that of rubidium, upon which the now-ubiquitous rubidium atomic clock time standard is based. Here we show that the ground state hyperfine populations of bismuth can be read out using the mid-infrared Rydberg transitions, analogous to the optical readout of the rubidium ground state populations upon which rubidium clock technology is based. We further use these transitions to demonstrate strong population pumping by resonant excitation of the bound exciton transitions, suggesting several possible approaches to a solid-state atomic clock using bismuth in silicon, or eventually in enriched 28Si

Picosecond Nonlinear Relaxation of Photoinjected Carriers in a Single GaAs/AlGaAs Quantum Dot

Photoemission from a single self-organized GaAs/AlGaAs quantum dot (QD) is temporally resolved with picosecond time resolution. The emission spectra consisting of the multiexciton structures are observed to depend on the delay time and the excitation intensity. Quantitative agreement is found between the experimental data and the calculation based on a model which characterizes the successive relaxation of multiexcitons. Through the analysis we can determine the carrier relaxation time as a function of population of photoinjected carriers. Enhancement of the intra-dot carrier relaxation is demonstrated to be due to the carrier-carrier scattering inside a single QD.Comment: 4 pages, 4 figures, to be published in Phys. Rev. B, Rapid

Coherent control of electron spin qubits in silicon using a global field

Silicon spin qubits promise to leverage the extraordinary progress in silicon nanoelectronic device fabrication over the past half century to deliver large-scale quantum processors. Despite the scalability advantage of using silicon technology, realising a quantum computer with the millions of qubits required to run some of the most demanding quantum algorithms poses several outstanding challenges, including how to control many qubits simultaneously. Recently, compact 3D microwave dielectric resonators were proposed as a way to deliver the magnetic fields for spin qubit control across an entire quantum chip using only a single microwave source. Although spin resonance of individual electrons in the globally applied microwave field was demonstrated, the spins were controlled incoherently. Here we report coherent Rabi oscillations of single electron spin qubits in a planar SiMOS quantum dot device using a global magnetic field generated off-chip. The observation of coherent qubit control driven by a dielectric resonator establishes a credible pathway to achieving large-scale control in a spin-based quantum computer

Short lifetime components in the relaxation of boron acceptors in silicon

We present time-resolved measurements of the relaxation between the orbital states of the shallow acceptor boron in silicon. The silicon host was enriched Si-28, which exhibits life-time broadened absorption lines. We observed a wide range of T1 lifetimes from 6ps to 130ps depending on the excited state and the pump intensity. The fastest transients have not been observed previously in the time domain, and they are caused by the phonon relaxation responsible for the small-signal frequency domain line-width. We identify the slower components with an ionisation/recombination/cascade pathway

High-purity, isotopically enriched bulk silicon

The synthesis and characterization of dislocation-free, undoped, single crystals of Si enriched in all 3 stable isotopes is reported: {sup 28}Si (99.92%), {sup 29}Si (91.37%), and {sup 30}Si (89.8%). A silane-based process compatible with the relatively small amounts of isotopically enriched precursors that are practically available was used. The silane is decomposed to silicon on a graphite starter rod heated to 700-750 C in a recirculating flow reactor. A typical run produces 35 gm of polycrystalline Si at a growth rates of 5 {micro}m/min and conversion efficiency >95%. Single crystals are grown by the floating zone method and characterized by electrical and optical measurements. Concentrations of shallow dopants (P and B) are as low as mid-10{sup 13} cm{sup -3}. Concentrations of C and O lie below 10{sup 16} and 10{sup 15} cm{sup -3}, respectively

Hyperfine Stark effect of shallow donors in silicon

We present a complete theoretical treatment of Stark effects in bulk doped silicon, whose predictions are supported by experimental measurements. A multivalley effective mass theory, dealing nonperturbatively with valley-orbit interactions induced by a donor-dependent central cell potential, allows us to obtain a very reliable picture of the donor wave function within a relatively simple framework. Variational optimization of the 1s donor binding energies calculated with a new trial wave function, in a pseudopotential with two fitting parameters, allows an accurate match of the experimentally determined donor energy levels, while the correct limiting behavior for the electronic density, both close to and far from each impurity nucleus, is captured by fitting the measured contact hyperfine coupling between the donor nuclear and electron spin. We go on to include an external uniform electric field in order to model Stark physics: with no extra ad hoc parameters, variational minimization of the complete donor ground energy allows a quantitative description of the field-induced reduction of electronic density at each impurity nucleus. Detailed comparisons with experimental values for the shifts of the contact hyperfine coupling reveal very close agreement for all the donors measured (P, As, Sb, and Bi). Finally, we estimate field ionization thresholds for the donor ground states, thus setting upper limits to the gate manipulation times for single qubit operations in Kane-like architectures: the Si:Bi system is shown to allow for A gates as fast as ≈10 MHz

Dal ketos al senmurv? Mutazioni iconografiche e transizioni simboliche del ketos dall'antichità al Medioevo (secolo XIII)

Using literary and iconographic sources the paper discusses the image of ketos from Antiquity to Middle Ages. The ketos, according with Greek literature, was used in the myths of both Perseus and Andromeda and Heracles and Hesione. The archaic images of the sea-monster are identifiable on Corinthian vases, on which we have only heads of leonine form. From 5th century the classical type of ketos is distinguished from all other Greek sea-monsters by a long neck, fins (also like wings), long muzzle and corrugated upper surface (like a crocodile), and leonine forelegs. Separated from histories of Andromeda and Hesione, the ketos is represented as a mount of marine gods and, especially, Nereides. The transition from Late Antiquity to Early Christian art is well represented by Aratea and by the Book of Jonah, on which the ketos was reproduced using the classic type. It served for representing Jonah’s big fish on sarcophagi and catacombs paintings, according to Midrash commentary who distinguished ketos from Leviathan. During the Middle Ages (from 11th-12th century) the image of ketos changed gradually in two directions: from classical type into a kind of a panther/dog, sometime winged, with a sea-serpent tale (Campanian ambos); or into a simple big fish as reproduced on manuscripts and italian sculptures. The article also discusses the influence of Sassanid Senmurv, concluding that the ketos was essentially an elaboration of models from Antiquity