Optical addressing of an individual erbium ion in silicon

The detection of electron spins associated with single defects in solids is a critical operation for a range of quantum information and measurement applications currently under development. To date, it has only been accomplished for two centres in crystalline solids: phosphorus in silicon using electrical readout based on a single electron transistor (SET) and nitrogen-vacancy centres in diamond using optical readout. A spin readout fidelity of about 90% has been demonstrated with both electrical readout and optical readout, however, the thermal limitations of the electrical readout and the poor photon collection efficiency of the optical readout hinder achieving the high fidelity required for quantum information applications. Here we demonstrate a hybrid approach using optical excitation to change the charge state of the defect centre in a silicon-based SET, conditional on its spin state, and then detecting this change electrically. The optical frequency addressing in high spectral resolution conquers the thermal broadening limitation of the previous electrical readout and charge sensing avoids the difficulties of efficient photon collection. This is done with erbium in silicon and has the potential to enable new architectures for quantum information processing devices and to dramatically increase the range of defect centres that can be exploited. Further, the efficient electrical detection of the optical excitation of single sites in silicon is a major step in developing an interconnect between silicon and optical based quantum computing technologies.Comment: Corrected the third affiliation. Corrected one cross-reference of "Fig. 3b" to "Fig. 3c". Corrected the caption of Fig. 3a by changing (+-)1 to

Strong Anisotropy in Liquid Water upon Librational Excitation using Terahertz Laser Fields

Tracking the excitation of water molecules in the homogeneous liquid is challenging due to the ultrafast dissipation of rotational excitation energy through the hydrogen-bonded network. Here we demonstrate strong transient anisotropy of liquid water through librational excitation using single-color pump-probe experiments at 12.3 THz. We deduce a third order response of chi^3 exceeding previously reported values in the optical range by three orders of magnitude. Using a theory that replaces the nonlinear response with a material response property amenable to molecular dynamics simulation, we show that the rotationally damped motion of water molecules in the librational band is resonantly driven at this frequency, which could explain the enhancement of the anisotropy in the liquid by the external Terahertz field. By addition of salt (MgSO4), the hydration water is instead dominated by the local electric field of the ions, resulting in reduction of water molecules that can be dynamically perturbed by THz pulses

Room temperature coherent control of coupled single spins in solid

Coherent coupling between single quantum objects is at the heart of modern quantum physics. When coupling is strong enough to prevail over decoherence, it can be used for the engineering of correlated quantum states. Especially for solid-state systems, control of quantum correlations has attracted widespread attention because of applications in quantum computing. Such coherent coupling has been demonstrated in a variety of systems at low temperature1, 2. Of all quantum systems, spins are potentially the most important, because they offer very long phase memories, sometimes even at room temperature. Although precise control of spins is well established in conventional magnetic resonance3, 4, existing techniques usually do not allow the readout of single spins because of limited sensitivity. In this paper, we explore dipolar magnetic coupling between two single defects in diamond (nitrogen-vacancy and nitrogen) using optical readout of the single nitrogen-vacancy spin states. Long phase memory combined with a defect separation of a few lattice spacings allow us to explore the strong magnetic coupling regime. As the two-defect system was well-isolated from other defects, the long phase memory times of the single spins was not diminished, despite the fact that dipolar interactions are usually seen as undesirable sources of decoherence. A coherent superposition of spin pair quantum states was achieved. The dipolar coupling was used to transfer spin polarisation from a nitrogen-vacancy centre spin to a nitrogen spin, with optical pumping of a nitrogen-vacancy centre leading to efficient initialisation. At the level anticrossing efficient nuclear spin polarisation was achieved. Our results demonstrate an important step towards controlled spin coupling and multi-particle entanglement in the solid state

Measurement of wavefunction overlap of phosphorus donors in silicon

© 2008 Dr. Nikolas StavriasThere are many formidable challenges along the road to building a silicon quantum computer, and perhaps none is more demanding than engineering and measuring the coupling between qubits. In the P donor implementation of a solid state quantum computer, entanglement is mediated via coupling between P donors. The exchange coupling interaction governs the two qubit interactions and the exchange energy sets a limit on the speed of the qubit interactions. Although the interaction has been extensively modelled, there are few techniques that can provide information as to the strength of the interaction. The study of donor-donor interactions is made difficult by the need to engineer and control the spacing between atoms. This thesis reports a novel approach to the creation of ensembles of pairs of donors using molecular ion implantation. The technique is consistent with the top-down strategy for the creation of qubits via low energy phosphorus ion implantation. While originally motivated by the measurement of the strength of the exchange coupling between phosphorus donor atoms via a proposal to use electronic Raman scattering, this thesis ended up studying the various components required of the measurement. These included the electronic Raman scattering technique, the accurate measurement of the sample temperature, and the production and analysis of samples containing closely spaced clusters of donors. The main results of this thesis are as follows: 1. Simulations of the ion implantation process were employed to calculate the expected distributions of the phosphorus donors following ion implantation. Monte Carlo simulations were compared to molecular dynamics simulations for both atomic and molecular dimer implantation. The degree of clustering of P donors into pairs and clusters containing more than two atoms was simulated for both molecular and atomic implantation. The results provide a set of simulation tools that provide a guide to the implantation parameters that are required to produce the required distribution of donors. 2. Electronic Raman scattering of phosphorus donors in silicon was evaluated as a technique to measure the exchange coupling between pairs of donors. Both visible and infra-red excitation was employed. For visible excitation, the electronic Raman transition was not observed due to competition with the much more efficient process of exciton generation and binding to donors. Measurements in the near infra-red revealed the electronic Raman scattering transition from both donors and acceptors in bulk doped silicon, but did not have the sensitivity to measure shallow implanted samples. It was not possible to determine the exchange coupling interaction using the available experimental set-up. 3. The measurement of exchange coupling requires the precise knowledge of the local sample temperature, and as laser heating can be an issue, a technique was required to provide a local temperature probe. The temperature dependence of the TO mode phonon was studied as a local probe of temperature for the cryogenically cooled samples. An anomalous shift in the temperature dependence of the frequency of the phonon was observed and reported for the first time. 4. Low temperature photoluminescence was used to evaluate the quality of the sample substrate and impurities introduced during sample processing. Photoluminescence measurements of the phosphorus ion implanted samples revealed a peak originating from clusters of phosphorus donors which shifted in energy with the density of phosphorus atoms. The behaviour of the peak was modelled using two donor interaction, but it was the many-particle process of band gap narrowing and the formation of a dopant band which fully explained the peak behaviour

Optical addressing of an individual erbium ion in silicon

The detection of electron spins associated with single defects in solids is a critical operation for a range of quantum information and measurement applications under development. So far, it has been accomplished for only two defect centres in crystallineThis work was financially supported by the ARC Centre of Excellence for Quantum Computation and Communication Technology (CE110001027) and the Future Fellowships (FT100100589 and FT110100919)

Transient transmission of THz metamaterial antennas by impact ionization in a silicon substrate

Contains fulltext : 229648.pdf (publisher's version ) (Open Access

Raman study on the phase transformations of the meta-stable phases of Si induced by indentation

Raman scattering is used to investigate the metastable Si phases formed by indentation. The indent strain, phase distribution and the kinetics of the phase transformations are examined

Photo-ionisation spectra of single erbium centres by charge sensing with a nano transistor

We show the photo-ionisation of an individual erbium centre in silicon. A single-electron transistor is used as a charge detector to observe the resonant ionization as a function of photon energy. This allows for optical addressing and electrical detection of individual erbium centres with exceptionally narrow line width