A5062425550- Quantum and electron transport phenomena
- Atomic and Subatomic Physics Research
- Quantum optics and atomic interactions
- Semiconductor Quantum Structures and Devices
- Dielectric materials and actuators
- Advanced Sensor and Energy Harvesting Materials
- Quantum Dots Synthesis And Properties
- GaN-based semiconductor devices and materials
- Graphene research and applications
- Semiconductor materials and devices
- High voltage insulation and dielectric phenomena
- Mechanical and Optical Resonators
- Molecular Junctions and Nanostructures
- Advanced Chemical Physics Studies
- Electron Spin Resonance Studies
- Physics of Superconductivity and Magnetism
- Acoustic Wave Resonator Technologies
- Metal and Thin Film Mechanics
- Silicon Nanostructures and Photoluminescence
- Spectroscopy and Laser Applications
- Advanced NMR Techniques and Applications
- Quantum Information and Cryptography
- Chalcogenide Semiconductor Thin Films
- Diamond and Carbon-based Materials Research
- Ferroelectric and Piezoelectric Materials
National Physical Laboratory
2022-2024
Tata Institute of Fundamental Research
2024
Vedanta Resources (India)
2023
Université Paris-Saclay
2017-2021
CEA Paris-Saclay
2017-2021
Centre National de la Recherche Scientifique
2003-2021
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2017-2021
University of Basel
2015-2018
North Carolina State University
2006-2016
Jawaharlal Nehru University
2016
A scheelite crystal with residual concentration of erbium is cooled down to 10 mK, yielding a record spin coherence time 23 ms.
We find, with the use of first-principles calculations, that single-atom-thick sp2-bonded noncentrosymmetric crystals like boron-nitride (BN) sheet exhibit an unusual nonlinear electromechanical effect: they become strongly macroscopically polarized in a corrugated state (or it induces significant changes initially BC2N). The direction induced polarization is plane film and depends nonanalytically on corrugation wave vector k. magnitude can reach very large values spite its quadratic...
We study spin relaxation and diffusion in an electron-spin ensemble of nitrogen impurities diamond at low temperature (0.25-1.2 K) polarizing magnetic field (80-300 mT). Measurements exploit field-controlled coupling the to two modes a transmission-line resonator. The observed temperature-independent time indicates that outdiffusion across mode volume dominates over spin-lattice relaxation. Depolarization one hyperfine-split subensemble by pumping another fast cross relaxation, with...
We present calculations of the transition energies and radiative lifetimes in GaN quantum dots embedded AlN. The effects elastic strains, piezoelectric pyroelectric fields are included. electronic structure is described using a tight-binding method which takes into account screening internal electric field by excited carriers fully self-consistent procedure. show that presence one electron-hole pair dot increases optical gap few tens meV decreases significantly lifetime, could give rise to...
The phase diagrams of polyvinylidene fluoride (PVDF) and its copolymers with chlorotrifluoroethylene (CTFE) are investigated by first-principles calculations. Both PVDF dilute P(VDF-CTFE) prefer nonpolar structures at zero field, but transform to a polar below the breakdown field. critical field decreases increasing CTFE content, facilitating transformation. In disordered P(VDF-CTFE), distribution concentrations leads range transitions, resulting in ultrahigh energy density. These results...
We report electron spin resonance measurements of donors in silicon at millikelvin temperatures using a superconducting $LC$ planar micro-resonator and Josephson Parametric Amplifier. The resonator includes nanowire inductor, defining femtoliter detection volume. Due to strain the substrate, donor lines are heavily broadened. Single-spin photon coupling strengths up $\sim 3~\text{kHz}$ observed. single shot sensitivity is $120 \pm 24~$spins/Hahn echo, corresponding $\approx 12...
Using first-principles simulations, we identify the microscopic origin of nonlinear dielectric response and high energy density polyvinylidene-fluoride-based polymers as a cooperative transition path that connects nonpolar polar phases system. This explores complex torsional rotational manifold is thermodynamically kinetically accessible at relatively low temperatures. Furthermore, introduction suitable copolymers significantly alters barriers between providing tunability both critical fields.
Coupling carbon nanotube devices to microwave circuits offers a significant increase in bandwidth (BW) and signal-to-noise ratio. These facilitate fast non-invasive readouts important for quantum information processing, shot noise correlation measurements. However, creation of device that unites low-disorder with low-loss resonator has so far remained challenge, due fabrication incompatibility one the other. Employing mechanical transfer method, we successfully couple gigahertz...
Local-density approximation calculations are performed to predict properties of compressively strained hexagonal ScN. This material is found exhibit a large electromechanical response, structural phase transition from nonpolar polar structure, and variation the band gap in entire visible light range when continuously changing compressive strain. Microscopic effects responsible for these anomalies revealed discussed. Suggestions on how practically grow ScN-based materials having such unusual...
In ab initio calculations of surfaces or nonperiodic systems, one frequently relies on the supercell approximation, where periodic replicas system are separated by enough empty space to avoid spurious interactions between successive images. However, a vacuum separation is not sufficient screen dipolar interaction that appears in asymmetrically charged polar systems. The dipole correction and Coulomb cutoff methods often used eliminate such replicas. this work, these compared under same...
We report long coherence times (up to 300 ms) for near-surface bismuth donor electron spins in silicon coupled a superconducting microresonator, biased at clock transition. This enables us demonstrate the partial absorption of train weak microwave fields spin ensemble, their storage 100 ms, and retrieval, using Hahn-echo-like protocol. Phase quantum statistics are preserved storage.
The size $(d)$ dependence of photoluminescence from nanocrystalline semiconductors is examined. overall luminescence determined by two distinct physical mechanisms: (i) the variation semiconductor gap with $d$ (typically $\ensuremath{\sim}{1/d}^{\ensuremath{\alpha}},$ $\ensuremath{\alpha}>1),$ and (ii) oscillator strength ${f}_{\mathrm{osc}}$ ${1/d}^{\ensuremath{\beta}},$ $5<~\ensuremath{\beta}<~6).$ We present an analytical framework to understand line shape based on above...
We study the hydrogenic impurity in a quantum dot (QD). employ effective mass theory with realistic barrier and variable mass. The model is simple, but it predicts features not previously observed. observe that shallow becomes deeper as size (R) reduced further reduction of at times resonant conduction band. Such shallow-deep (SHADE) transition investigated critical terms Bohr radius (aI*) identified. A relevant aspect QD dielectric constant, ε, its decreases. Employing dependent ε(R), we...
First-principles calculations have been carried out to reveal structural, electromechanical, electronic, and lattice dynamical properties of $\mathrm{GaN}∕\mathrm{ScN}$ $\mathrm{InN}∕\mathrm{ScN}$ superlattices---made by alternating hexagonal layers GaN, or InN, with ScN---for different periods overall compositions. These nitride systems belong two structural classes (having coordination number), depending on the composition. For Sc compositions larger than 50%, each atom has nearly five...
Nanoscale-resolved dielectric properties of polypropylene/metal-oxide (alumina, ${\text{PbTiO}}_{3}$) interfaces and the corresponding surfaces are investigated via first-principles calculations. In order to ascertain locality atomically resolved permittivity profiles, we propose a simple procedure directly evaluate real-space decay length nonlocal effects in susceptibility. Based on this length, microscopic response is derived by using convolution rectangular Gaussian filters as averaging...
We describe a nonlinear interaction between charge currents and spin which arises from the energy dependence of conductivity. This allows nonmagnetic contacts to be used for measuring controlling signals. choose graphene as model system study these effects predict its magnitudes in nonlocal valve devices. The ambipolar behavior is demonstrate amplification accumulation p-n junctions by applying current through contacts.
In high sensitivity inductive electron spin resonance spectroscopy, superconducting microwave resonators with large quality factors are employed. While they enhance the sensitivity, also distort considerably shape of applied rectangular control pulses, which limits degree over ensemble. Here, we employ shaped pulses compensating signal distortion to drive spins faster than resonator bandwidth. This translates into a shorter echo, enhanced signal-to-noise ratio. The useful minimize dead-time...
Abstract. We report measurements of electron-spin-echo envelope modulation (ESEEM) performed at millikelvin temperatures in a custom-built high-sensitivity spectrometer based on superconducting micro-resonators. The high quality factor and small mode volume (down to 0.2 pL) the resonator allow us probe number spins, down 5×102. measure two-pulse ESEEM two systems: erbium ions coupled 183W nuclei natural-abundance CaWO4 crystal bismuth donors residual 29Si silicon substrate that was...
The demand for a fast high-frequency read-out of high impedance devices, such as quantum dots, necessitates matching. Here we use resonant matching circuit (a stub tuner) realized by on-chip superconducting transmission lines to measure the electronic shot noise carbon nanotube dot at frequency close 3 GHz in an efficient way. As compared wide-band detection without matching, signal ratio can be enhanced much factor 800 device with 100 k$\Omega$. advantage resonator concept is ease which...
The ability to control microwave emission from a spin ensemble is requirement of several quantum memory protocols. Here, we demonstrate such by using resonator whose frequency can be rapidly tuned with bias current. We store excitations in an rare-earth ions and suppress on demand the echo (``echo silencing'') two methods: (1) detuning during rephasing, (2) subjecting spins magnetic field gradients generated current itself. also show that coherence preserved silencing.