Alexander Stark, Nati Aharon, Alexander Huck, Haitham A. R El-Ella, Alex Retzker, Fedor Jelezko, and Ulrik L. Andersen. 10/4/2018. “Clock transition by continuous dynamical decoupling of a three-level system.” Scientific Reports, 8. Publisher's Version Abstract
We present a novel continuous dynamical decoupling scheme for the construction of a robust qubit in a three-level system. By means of a clock transition adjustment, we first show how robustness to environmental noise is achieved, while eliminating drive-noise, to first-order. We demonstrate this scheme with the spin sub-levels of the NV-centre’s electronic ground state. By applying drive fields with moderate Rabi frequencies, the drive noise is eliminated and an improvement of 2 orders of magnitude in the coherence time is obtained compared to the pure dephasing time. We then show how the clock transition adjustment can be tuned to eliminate also the second-order effect of the environmental noise with moderate drive fields. A further detailed theoretical investigation suggests an additional improvement of more than 1 order of magnitude in the coherence time which is supported by simulations. Hence, our scheme predicts that the coherence time may be prolonged towards the lifetime-limit using a relatively simple experimental setup.
Nils Scharnhorst, Javier Cerrillo, Johannes Kramer, Ian D. Leroux, Jannes B. Wübbena, Alex Retzker, and Piet O. Schmidt. 8/27/2018. “Experimental and theoretical investigation of a multimode cooling scheme using multiple electromagnetically-induced-transparency resonances.” Physical Review a, 98, 2. Publisher's Version Abstract
We introduce and demonstrate double-bright electromagnetically-induced-transparency (D-EIT) cooling as an extension to EIT cooling. By involving an additional ground state, two bright states can be shifted individually into resonance for cooling of motional modes of frequencies that may be separated by more than the width of a single EIT cooling resonance. This allows three-dimensional ground-state cooling of a 40Ca+ ion trapped in a linear Paul trap with a single cooling pulse. Measured cooling rates and steady-state mean motional quantum numbers for this D-EIT cooling are compared with those of standard EIT cooling as well as concatenated standard EIT cooling pulses for multimode cooling. Experimental results are compared to full-density matrix calculations. We observe a failure of the theoretical description within the Lamb-Dicke regime that can be overcome by a time-dependent rate theory. Limitations of the different cooling techniques and possible extensions to multi-ion crystals are discussed.
Tuvia Gefen, Maxim Khodas, Liam P. McGuinness, Fedor Jelezko, and Alex Retzker. 7/27/2018. “Quantum spectroscopy of single spins assisted by a classical clock.” Physical Review a, 98, 1. Publisher's Version Abstract
Quantum spectroscopy with single two-level systems has considerably improved our ability to detect weak signals. Recently it was realized that for classical signals, precision and resolution of quantum spectroscopy is limited mainly by coherence of the signal and the stability of the clock used to measure time. The coherence time of the quantum probe, which can be significantly shorter, is not a major limiting factor in resolution measurements. Here, we address a similar question for spectroscopy of quantum signals, for example, a quantum sensor is used to detect a single nuclear spin. We present and analyze a novel correlation spectroscopy technique with performance that is limited by the coherence time of the target spins and the stability of the clock.
P Fernandez-Acebal, O Rosolio, J Scheuer, C Muller, S Muller, S Schmitt, LP McGuinness, I Schwarz, Q Chen, A Retzker, B Naydenov, F Jelezko, and MB Plenio. 2/22/2018. “Toward Hyperpolarization of Oil Molecules via Single Nitrogen Vacancy Centers in Diamond.” Nano Letters, 18, 3, Pp. 1882-1887. Publisher's Version Abstract
Efficient polarization of organic molecules is of extraordinary relevance when performing nuclear magnetic resonance (NMR) and imaging. Commercially available routes to dynamical nuclear polarization (DNP) work at extremely low temperatures, relying on the solidification of organic samples and thus bringing the molecules out of their ambient thermal conditions. In this work, we investigate polarization transfer from optically pumped nitrogen vacancy centers in diamond to external molecules at room temperature. This polarization transfer is described by both an extensive analytical analysis and numerical simulations based on spin bath bosonization and is supported by experimental data in excellent agreement. These results set the route to hyperpolarization of diffusive molecules in different scenarios and consequently, due to an increased signal, to high-resolution NMR.
J Cerrillo, A Retzker, and MB Plenio. 7/30/2018. “Double-path dark-state laser cooling in a three-level system.” Physical Review a, 98, 1. Publisher's Version Abstract
We present a detailed analysis of a robust and fast laser cooling scheme [J. Cerrillo et al., Phys. Rev. Lett. 104, 043003 (2010)] on a three-level system. A special laser configuration, applicable to trapped ions, atoms, or cantilevers, designs a double-path quantum interference that eliminates the blue sideband in addition to the carrier transition, thus excluding any heating process involving up to one-phonon interactions. As a consequence, cooling achieves vanishing phonon occupation up to first order in the Lamb-Dicke parameter expansion. Underlying this scheme is a combined action of two cooling schemes which makes the proposal very flexible under constraints of the physical parameters such as laser intensity, detuning, or optical access, making it a viable candidate for experimental implementation. Furthermore, it is considerably faster than existing ground state cooling schemes. Its suitability as a cooling scheme for several ions in a trap and three-dimensional cooling is shown.