M. Steger

Quantum information storage for over 180 s using donor spins in a 28si “semiconductor vacuum”

Extending Quantum Memory Practical applications in quantum communication and quantum computation require the building blocks—quantum bits and quantum memory—to be sufficiently robust and long-lived to allow for manipulation and storage (see the Perspective by Boehme and McCarney). Steger et al. (p. 1280) demonstrate that the nuclear spins of 31P impurities in an almost isotopically pure sample of 28Si can have a coherence time of as long as 192 seconds at a temperature of ∼1.7 K. In diamond at room temperature, Maurer et al. (p. 1283) show that a spin-based qubit system comprised of an isotopic impurity (13C) in the vicinity of a color defect (a nitrogen-vacancy center) could be manipulated to have a coherence time exceeding one second. Such lifetimes promise to make spin-based architectures feasible building blocks for quantum information science. An almost isotopically pure sample of 28Si provides a vacuumlike environment for 31P qubits. A quantum computer requires systems that are isolated from their environment, but can be integrated into devices, and whose states can be measured with high accuracy. Nuclear spins in solids promise long coherence lifetimes, but they are difficult to initialize into known states and to detect with high sensitivity. We show how the distinctive optical properties of enriched 28Si enable the use of hyperfine-resolved optical transitions, as previously applied to great effect for isolated atoms and ions in vacuum. Together with efficient Auger photoionization, these resolved hyperfine transitions permit rapid nuclear hyperpolarization and electrical spin-readout. We combine these techniques to detect nuclear magnetic resonance from dilute 31P in the purest available sample of 28Si, at concentrations inaccessible to conventional measurements, measuring a solid-state coherence time of over 180 seconds.

Strain balanced InAs/InAsSb superlattice structures with optical emission to 10 μm

We report the growth and optical characterization of InAsSb/InAs strain balanced superlattice structures on GaSb substrates for potential application in midinfrared photodetectors. Photoluminescence (PL) emission was observed in the range 5u2002μm≤λ≤10u2002μm at 4 K for Sb compositions 0.14≤xSb≤0.27. The PL energy was found to depend approximately linearly on antimony, consistent with a type II band lineup. The dependence of the emission energies on the Sb mole fraction is in agreement with trends predicted by various theoretical works. The data suggest that this transition reaches zero energy for a composition of xSb=0.37.

Hyperfine structure and nuclear hyperpolarization observed in the bound exciton luminescence of Bi donors in natural Si.

As the deepest group-V donor in Si, Bi has by far the largest hyperfine interaction and also a large I = 9/2 nuclear spin. At zero field this splits the donor ground state into states having total spin 5 and 4, which are fully resolved in the photoluminescence spectrum of Bi donor bound excitons. Under a magnetic field, the 60 expected allowed transitions cannot be individually resolved, but the effects of the nuclear spin distribution, -9/2 < or = I(z) < or = 9/2, are clearly observed. A strong hyperpolarization of the nuclear spin towards I(z) = -9/2 is observed to result from the nonresonant optical excitation. This is very similar to the recently reported optical hyperpolarization of P donors observed by EPR at higher magnetic fields. We introduce a new model to explain this effect, and predict that it may be very fast.

Homogeneous linewidth of the P31 bound exciton transition in silicon

The optical transitions of the shallow donor bound exciton associated with phosphorus in silicon are a subject of renewed interest due to the recent discovery that these transitions can be used to both read out and initialize the donor electron and nuclear spin in highly enriched S28i. The ultimate limit of these processes will be determined by the natural or homogeneous linewidth which we determine here using spectral hole burning. The observed 10 neV linewidth is only four times the limit set by the bound exciton lifetime.

Shallow Impurity Absorption Spectroscopy in Isotopically Enriched Silicon

Karaiskaj et al. showed that the isotopic randomness present in natural Si (natSi) causes inhomogeneous broadening of many of the ground state to excited state infrared absorption transitions of the shallow donor phosphorous and acceptor boron. This was surprising since it was thought that the observed linewidths of shallow impurities in silicon are at their fundamental lifetime limit. We report improved high‐resolution infrared absorption studies of these impurities in isotopically enriched 28Si, 29Si and 30Si. The new data improves on the linewidths of earlier spectra due to reduced concentration broadening. Some of the transitions in 28Si show the narrowest FWHM ever reported for shallow donor and acceptor absorption transitions.

Nuclear Polarization of Phosphorus Donors in 28Si by Selective Optical Pumping

We show that significant electronic and nuclear polarizations of 31P donors in highly enriched 28Si can be obtained by dynamic optical pumping. Polarization of the donor spins is observed using photoluminescence excitation spectroscopy and optical pumping of individual hyperfine components of the 31P bound exciton transition. Previous samples of 28Si used for 31P bound exciton spectroscopy were p‐type due to excess boron, while more recently, samples of 31P‐doped n‐type 28Si with 99.99% isotopic purity became available. The selective pumping and ionization of 31P donors in specific electronic and nuclear spin states has applications in quantum computing, where a highly polarized initial state is required.

Spin relaxation and donor-acceptor recombination of Se + in 28-silicon

Selenium impurities in silicon are deep double donors and their optical and electronic properties have been recently investigated due to their application for infrared detection. However, a singly ionized selenium donor (Se + )possessesanelectronspinwhichmakesitapotentialcandidateasasilicon-basedspinqubit,withsignificant potential advantages compared to the more commonly studied group V donors. Here we study the electron spin relaxation (T1) and coherence (T2) times of Se + in isotopically purified 28-silicon, and find them to be up to two orders of magnitude longer than shallow group V donors at temperatures above ∼15 K. We further study the dynamics of donor-acceptor recombination between selenium and boron, demonstrating that it is possible to control the donor charge state through optical excitation of neutral Se 0 .

High Resolution Photoluminescence of Copper, Silver, Gold and Lithium‐related Isoelectronic Bound Excitons in Highly Enriched 28Si

Isotopic fingerprints of Li, Cu, Ag and Au in IBE centers are observed. A family of 4‐centers is suggested.