Strongly nonlinear antiferromagnetic dynamics in high magnetic fields

Antiferromagnetic (AFM) materials possess a well-recognized potential for ultrafast data processing thanks to their intrinsic ultrafast spin dynamics, absence of stray fields, and large spin transport effects. The very same properties, however, make their manipulation difficult, requiring frequencies in THz range and magnetic fields of tens of Teslas. Switching of AFM order implies going into the nonlinear regime, a largely unexplored territory. Here we use THz light from a free electron laser to drive antiferromagnetic NiO into a highly nonlinear regime and steer it out of nonlinearity with magnetic field from a 33-Tesla Bitter magnet. This demonstration of large-amplitude dynamics represents a crucial step towards ultrafast resonant switching of AFM order.Antiferromagnetic (AFM) materials possess a well-recognized potential for ultrafast data processing thanks to their intrinsic ultrafast spin dynamics, absence of stray fields, and large spin transport effects. The very same properties, however, make their manipulation difficult, requiring frequencies in THz range and magnetic fields of tens of Teslas. Switching of AFM order implies going into the nonlinear regime, a largely unexplored territory. Here we use THz light from a free electron laser to drive antiferromagnetic NiO into a highly nonlinear regime and steer it out of nonlinearity with magnetic field from a 33-Tesla Bitter magnet. This demonstration of large-amplitude dynamics represents a crucial step towards ultrafast resonant switching of AFM order

Room temperature quantum bit storage exceeding 39 minutes using ionized donors in 28-silicon

Quantum memories capable of storing and retrieving coherent information for extended times at room temperature would enable a host of new technologies. Electron and nuclear spin qubits using shallow neutral donors in semiconductors have been studied extensively but are limited to low temperatures ($\le$10 K); however, the nuclear spins of ionized donors have potential for high temperature operation. We use optical methods and dynamical decoupling to realize this potential for an ensemble of 31P donors in isotopically purified 28Si and observe a room temperature coherence time of over 39 minutes. We further show that a coherent spin superposition can be cycled from 4.2 K to room temperature and back, and report a cryogenic coherence time of 3 hours in the same system.Comment: 5 pages, 4 figure

Radio frequency measurements of tunnel couplings and singlet–triplet spin states in Si:P quantum dots

Spin states of the electrons and nuclei of phosphorus donors in silicon are strong candidates for quantum information processing applications given their excellent coherence times. Designing a scalable donor-based quantum computer will require both knowledge of the relationship between device geometry and electron tunnel couplings, and a spin readout strategy that uses minimal physical space in the device. Here we use radio frequency reflectometry to measure singlet–triplet states of a few-donor Si:P double quantum dot and demonstrate that the exchange energy can be tuned by at least two orders of magnitude, from 20 μeV to 8 meV. We measure dot–lead tunnel rates by analysis of the reflected signal and show that they change from 100 MHz to 22 GHz as the number of electrons on a quantum dot is increased from 1 to 4. These techniques present an approach for characterizing, operating and engineering scalable qubit devices based on donors in silicon

Optical NMR Study of 31P Donor Spins in Isotopically Enriched 28Si

A quantum computer requires a quantum system that is isolated from its environment, but can be integrated into devices, and whose states can be measured with high accuracy. Nuclear spin qubits using shallow neutral donors in semiconductors have been studied extensively as quantum memories due to their promise of long coherence lifetimes. However, the nuclear spins of neutral donors are not only difficult to initialize into known states and detect with high sensitivity, they are limited to use at cryogenic temperatures. The nuclear spins of ionized donors, on the other hand, have the potential for high-temperature operation. In this thesis, I show how the distinctive optical properties of enriched 28Si enable the use of hyperfine-resolved optical transitions of donor bound excitons, as previously applied to great effect for isolated atoms and ions in vacuum. Together with efficient Auger photoionization, these optical transitions permit rapid nuclear hyperpolarization and electrical spin readout. These techniques are combined to detect nuclear magnetic resonance from dilute 31P in an isotopically purified 28Si sample, at concentrations inaccessible to conventional NMR techniques. Dynamical decoupling is used to measure cryogenic coherence times of over 180 seconds and 3 hours for an ensemble of neutral and ionized 31P nuclear spins in 28Si, respectively. A room-temperature coherence time of over 39 minutes is demonstrated in the latter system, which is more than an order of magnitude longer than the previous solid-state coherence time record. I further show that a coherent spin superposition can be cycled from 4.2 Kelvin to room temperature and back

Highly efficient THz four-wave mixing in doped silicon

Third-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica. Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility χ(3)L (where L represents the material thickness) as well as technological possibilities such as optically gated detection and emission of photons. Using picosecond pulses from a free electron laser, we show that silicon doped with P or Bi has a value of χ(3)L in the THz domain that is higher than that reported for any other material in any wavelength band. The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion (also a χ(3) process), and they open the door to exploitation of non-degenerate mixing and optical nonlinearities beyond the perturbative regime