S. A. Lyon

Princeton University, Princeton, New Jersey, United States

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Publications (193)491.8 Total impact

  • Maika Takita, S. A. Lyon
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    ABSTRACT: Electrons floating on the surface of superfluid helium have been suggested as promising mobile spin quantum bits (qubits). Transferring electrons extremely efficiently in a narrow channel structure with underlying gates has been demonstrated, showing no transfer error while clocking $10^9$ pixels in a 3-phase charge coupled device (CCD). While on average, one electron per channel was clocked, it is desirable to reliably obtain a single electron per channel. We have designed an electron turnstile consisting of a narrow (0.8$\mu$m) channel and narrow underlying gates (0.5$\mu$m) operating across seventy-eight parallel channels. Initially, we find that more than one electron can be held above the small gates. Underlying gates in the turnstile region allow us to repeatedly split these electron packets. Results show a plateau in the electron signal as a function of the applied gate voltages, indicating quantization of the number of electrons per pixel, simultaneously across the seventy-eight parallel channels.
    10/2014;
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    ABSTRACT: The effects of host isotope mass on the hyperfine interaction of group-V donors in silicon are revealed by pulsed electron nuclear double resonance (ENDOR) spectroscopy of isotopically engineered Si single crystals. Each of the hyperfine-split P-31, As-75, Sb-121, Sb-123, and Bi-209 ENDOR lines splits further into multiple components, whose relative intensities accurately match the statistical likelihood of the nine possible average Si masses in the four nearest-neighbor sites due to random occupation by the three stable isotopes Si-28, Si-29, and Si-30. Further investigation with P-31 donors shows that the resolved ENDOR components shift linearly with the bulk-averaged Si mass.
    Physical Review B 09/2014; 90(12):121203(R). · 3.66 Impact Factor
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    ABSTRACT: Dopants in silicon have been studied for many decades using optical and electron spin resonance (ESR) spectroscopy. Recently, new features have been observed in the spectra of dopants in isotopically enriched 28Si since the reduced inhomogenous linewidth in this material improves spectral resolution. With this in mind, we measured ESR on exchange coupled phosphorus dimers in 28Si and report two results. First, a new fine structure is observed in the ESR spectrum arising from state mixing by the hyperfine coupling to the 31P nuclei, which is enhanced when the exchange energy is comparable to the Zeeman energy. Secondly, the average spin relaxation times, T1 and T2 of dimers with exchange coupling ranging from approximately 6 to 60 GHz were measured using pulsed ESR at 0.35 T. Both T1 and T2 were found to be identical to the relaxation times of isolated phosphorus donors in 28Si, with T2 = 3 ms at 5 K limited by spectral diffusion due to dipolar interactions with neighboring donor electron spins. This result, consistent with theoretical predictions, implies that an exchange coupling of 6-60 GHz does not limit the dimer T1 and T2 at the 10 ms timescale.
    09/2014;
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    ABSTRACT: We report the use of novel, capacitively terminated coplanar waveguide (CPW) resonators to measure the Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift dependent on electric and magnetic field orientations relative to the Si crystal. Using the measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. By measuring the linear Stark effect, we show that such sources of decoherence can be non-negligible due to strain. From our data, we estimate the effective electric field due to strain in our samples. Values for the spin-orbit and hyperfine Stark parameters are reported.
    09/2014;
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    ABSTRACT: We present a complete theoretical treatment of Stark effects in doped silicon, whose predictions are supported by experimental measurements. A multi-valley effective mass theory, dealing non-perturbatively with valley-orbit interactions induced by a donor-dependent central cell potential, allows us to obtain a very reliable picture of the donor wave function within a relatively simple framework. Variational optimization of the 1s donor binding energies calculated with a new trial wave function, in a pseudopotential with two fitting parameters, allows an accurate match of the experimentally determined donor energy levels, while the correct limiting behavior for the electronic density, both close to and far from each impurity nucleus, is captured by fitting the measured contact hyperfine coupling between the donor nuclear and electron spin. We go on to include an external uniform electric field in order to model Stark physics: With no extra ad hoc parameters, variational minimization of the complete donor ground energy allows a quantitative description of the field-induced reduction of electronic density at each impurity nucleus. Detailed comparisons with experimental values for the shifts of the contact hyperfine coupling reveal very close agreement for all the donors measured (P, As, Sb and Bi). Finally, we estimate field ionization thresholds for the donor ground states, thus setting upper limits to the gate manipulation times for single qubit operations in Kane-like architectures: the Si:Bi system is shown to allow for A gates as fast as around 10 MHz.
    08/2014;
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    ABSTRACT: We demonstrate the use of high-Q superconducting coplanar waveguide (CPW) microresonators to perform rapid manipulations on a randomly distributed spin ensemble using very low microwave power (400 nW). This power is compatible with dilution refrigerators, making microwave manipulation of spin ensembles feasible for quantum computing applications. We also describe the use of adiabatic microwave pulses to overcome microwave magnetic field ($B_{1}$) inhomogeneities inherent to CPW resonators. This allows for uniform control over a randomly distributed spin ensemble. Sensitivity data are reported showing a single shot (no signal averaging) sensitivity to $10^{7}$ spins or $3 \times 10^{4}$ spins/$\sqrt{Hz}$ with averaging.
    02/2014;
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    ABSTRACT: We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures, and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified $^{28}$Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to $\sim$ 2 V/$\mu$m to be applied across the SOI layer. Utilizing this structure we measure the Stark shift parameters of arsenic donors embedded in the $^{28}$Si SOI layer and find a contact hyperfine Stark parameter of $\eta_a=-1.9\pm0.2\times10^{-3} \mu$m$^2$/V$^2$. We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance.
    01/2014;
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    ABSTRACT: We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified 28Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to 2 V/μm to be applied across the SOI layer. Utilizing this structure, we measure the Stark shift parameters of arsenic donors embedded in the 28Si-SOI layer and find a contact hyperfine Stark parameter of ηa = −1.9 ± 0.7 × 10−3 μm2/V2. We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance.
    Applied Physics Letters 01/2014; 104(19):193502-193502-4. · 3.79 Impact Factor
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    ABSTRACT: Donors in silicon are now demonstrated as one of the leading candidates for implementing qubits and quantum information processing. Single qubit operations, measurements and long coherence times are firmly established, but progress on controlling two qubit interactions has been slower. One reason for this is that the inter donor exchange coupling has been predicted to oscillate with separation, making it hard to estimate in device designs. We present a multi-valley effective mass theory of a donor pair in silicon, including both a central cell potential and the effective mass anisotropy intrinsic in the Si conduction band. We are able to accurately describe the single donor properties of valley-orbit coupling and the spatial extent of donor wave functions, leading to hyperfine interaction values in close agreement with experiment. Ours is a simple framework that can be applied flexibly to a range of experimental scenarios, but it is nonetheless able to provide fast and reliable predictions. We use it to estimate the exchange coupling between two donor electrons and we find a smoothing of its expected oscillations, and predict a monotonic dependence on separation if two donors are spaced precisely along the [100] direction.
    12/2013;
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    ABSTRACT: A major challenge in using spins in the solid state for quantum technologies is protecting them from sources of decoherence. This is particularly important in nanodevices where the proximity of material interfaces, and their associated defects, can play a limiting role. Spin decoherence can be addressed to varying degrees by improving material purity or isotopic composition, for example, or active error correction methods such as dynamic decoupling (or even combinations of the two). However, a powerful method applied to trapped ions in the context of atomic clocks is the use of particular spin transitions that are inherently robust to external perturbations. Here, we show that such 'clock transitions' can be observed for electron spins in the solid state, in particular using bismuth donors in silicon. This leads to dramatic enhancements in the electron spin coherence time, exceeding seconds. We find that electron spin qubits based on clock transitions become less sensitive to the local magnetic environment, including the presence of (29)Si nuclear spins as found in natural silicon. We expect the use of such clock transitions will be of additional significance for donor spins in nanodevices, mitigating the effects of magnetic or electric field noise arising from nearby interfaces and gates.
    Nature Nanotechnology 06/2013; · 31.17 Impact Factor
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    ABSTRACT: NMR data from degenerately doped Si:P has suggested that the coherence of ^31P nuclear spins can be limited to a few ms in natural Si by spectral diffusion from ^29Si [1]. Here we report measurements of the nuclear spin coherence of neutral isolated ^31P donors in lightly-doped (˜10^15 /cm^3) Si with ^29Si concentrations from 1% to 50%. Pulsed ENDOR at X-band microwave frequency and a magnetic field of 0.35 T was used to measure the nuclear spins. The light doping and measurement temperature of 1.7K ensured that neither electron spin flips nor flip-flops limited the nuclear T2. We find that the resulting echo intensity decays are nonexponential, and the time to reach 1/e is inversely proportional to the ^29Si density. The nuclear decoherence time for natural silicon is found to be approximately 1 second, about 2000 times longer than donor electron spins in natural Si.[4pt] [1] G.P. Carver et al., Phys. Rev. B 3, 4285 (1971).
    03/2013;
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    ABSTRACT: Recently nitrogen-vacancy (NV) color centers in diamond have become the focus of many studies aimed towards their use as quantum bits (qubits) in quantum computing applications and as precision magnetic field sensors in scanned imaging applications. The NVs have a ground triplet state (S=1) with ZFS of 2.88 GHz. It has been previously shown that optical excitation, when shining green light at low magnetic fields (below 100 G), polarizes spins preferentially into the T0 state. Here we will report an X-band pulsed ESR measurement and demonstrate that the optical spin polarization is more complex at higher magnetic fields (3400 G) and can lead to preferential spin polarization into T+ and T- states, instead of T0. This effect can be understood from a simple one electron spin Hamiltonian and depends mainly on the relative orientation of the ZFS and external magnetic field. In addition, we observe strong ESEEM effects originating from the central nitrogen nucleus which are most prominent when measuring the T0 to T- transition and when the field is along the ZFS. From the orientation dependence of ESEEM we are able to accurately determine the nitrogen hyperfine and nuclear quadrupole tensors. Spin coherence of 0.8 ms is seen at 10 K, limited by 1 percent of magnetic ^13C nuclei in our natural diamond sample.
    03/2013;
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    ABSTRACT: Single electron spin states in Si/SiGe quantum dots have shown promise as qubits for quantum information processing. Recently, electron spins in gated Si/SiGe quantum dots have displayed relaxation (T1) and coherence (T2) times of 250 μs at 350mK. The experiments used conventional X-band (10 GHz) pulsed Electron Spin Resonance (pESR) on a large area (3.5 x 20 mm^2), double gated, undoped Si/SiGe heterostructure, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots with 150 nm radii and 700 nm period are induced in a natural Si quantum well by the gates. Smaller dots are expected to reduce the effects of nearly degenerate valley states and spin-orbit coupling on the electron spin coherence. However, the small number of spins makes signal recovery extremely challenging. We have implemented a broadband cryogenic HEMT low-noise-amplifier and a high-speed single-pole double-throw switch operating at liquid helium temperatures. The switch and preamp have improved our signal to noise by an order of magnitude, allowing for smaller samples and shorter measurement times. We will describe these improvements and the data they have enabled.
    03/2013;
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    ABSTRACT: Hybrid quantum devices where electron spins are used for state initialization, fast manipulation, long range entanglement and detection, while nuclear spins are used for long term storage promise revolutionary advantages. Here we report our first experiments using a silicon-based device that utilizes electron and nuclear spins of arsenic donors. The device is a large-area, parallel-plate capacitor fabricated on a silicon-on-insulator (SOI) wafer where the SOI layer is implanted with arsenic donors, and a back gate is formed in the silicon below the buried oxide by a high-energy boron implantation. The electrons can be controllably stripped from the donors and then reintroduced to the ionized donors by applying appropriate gate voltages. We use ensemble ESR experiments (X-band, magnetic field of 0.35 T) to track the occupancy of the donors during these operations. Pulsed ESR is used to characterize the spin state of the donor electrons and the effect of applied electric fields below the ionization threshold. The spin state of the arsenic nuclei, and the effect of electron removal and reintroduction on the nuclear state is expected to be observable in pulsed ENDOR experiments. The work is funded by LPS and NSF-MWN.
    03/2013;
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    ABSTRACT: Superconducting coplanar waveguide (CPW) resonators are a promising alternative to conventional volume resonators for electron spin resonance (ESR) experiments where the sample volume and thus the number of spins is small. However, the magnetic fields required for ESR could present a problem for Nb superconducting resonators, which can be driven normal. Very thin Nb films (50 nm) and careful alignment of the resonators parallel to the magnetic field avoid driving the Nb normal, but flux trapping can still be an issue. Trapped flux reduces the resonator Q-factor, can lead to resonant frequency instability, and can lead to magnetic field inhomogeneities. At temperatures of 1.9 K and in a magnetic field 0.32 T, we have tested X-band resonators fabricated directly on the surface of a silicon sample. Q-factors in excess of 15,000 have been obtained. A thin layer of GE varnish applied directly to the resonator has been used to glue a sapphire wafer to its surface, and we still find Q-factors of 16,000 or more in the 0.32 T field. ESR applications of these resonators will be discussed.
    03/2013;
  • Maika Takita, E. Y. Huang, S. A. Lyon
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    ABSTRACT: Electrons floating on the surface of superfluid helium have been suggested as promising mobile spin qubits, and they have shown extremely efficient transport above micron-sized helium-filled channels. While the calculated spin decoherence and relaxation times on helium are long, no experimental measurements have been made. Efficient thermalization of the spins is necessary for ESR measurements of their coherence, and a lack of thermalization has hindered these experiments. Bringing electrons onto a thin helium film above a metallic layer will speed spin relaxation due to Johnson noise current in the metal. At the same time, higher electron densities can be supported by thin helium films. Ideally, the electrons could be thermalized on the thin helium film coating a metal surface, and then moved to a helium-filled channel for electrical measurements of their density and the spin measurements. However roughness of the metal surface severely limits the electron mobility. Preliminary work show that electrons can be transported from one channel, across a helium-coated metal layer, and to the neighboring channel, by creating a smooth transition from the channel to the thin film.
    03/2013;
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    ABSTRACT: We discuss the design and implementation of thin film superconducting coplanar waveguide micro-resonators for pulsed electron spin resonance experiments. The performance of the resonators with P doped Si epilayer samples is compared to waveguide resonators under equivalent conditions. The high achievable filling factor even for small sized samples and the relatively high Q-factor result in a sensitivity of 4.5 × 10 spins per shot, which is superior to that of conventional waveguide resonators, in particular to spins close to the sample surface. The peak microwave power is on the order of a few milliwatts, which is compatible with measurements at ultra-low temperatures. We also discuss the effect of the nonuniform microwave magnetic field on the Hahn echo power dependence.
    The Review of scientific instruments 02/2013; 84(2):025116. · 1.52 Impact Factor
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    ABSTRACT: Bismuth (209Bi) is the deepest Group V donor in silicon and possesses the most extreme characteristics such as a 9/2 nuclear spin and a 1.5 GHz hyperfine coupling. These lead to several potential advantages for a Si:Bi donor electron spin qubit compared to the more common phosphorus donor. Previous studies on Si:Bi have been performed using natural silicon where linewidths and electron spin coherence times are limited by the presence of 29Si impurities. Here we describe electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) studies on 209Bi in isotopically pure 28Si. ESR and ENDOR linewidths, transition probabilities and coherence times are understood in terms of the spin Hamiltonian parameters showing a dependence on field and mI of the 209Bi nuclear spin. We explore various decoherence mechanisms applicable to the donor electron spin, measuring coherence times up to 700 ms at 1.7 K at X-band, comparable with 28Si:P. The coherence times we measure follow closely the calculated field-sensitivity of the transition frequency, providing a strong motivation to explore 'clock' transitions where coherence lifetimes could be further enhanced.
    Physical review. B, Condensed matter 07/2012; 86(24). · 3.77 Impact Factor
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    ABSTRACT: The ESR response from highly metal-semiconductor (M-SC) separated single-walled carbon nanotubes (SWCNTs) for temperatures T between 0.39 and 200 K is characteristically different for the two systems. The signal originates from defect spins but interaction with free electrons leads to a larger linewidth for M tubes. The latter decreases with increasing T, whereas it increases with T for SC tubes. The spins undergo a ferromagnetic phase transition below around 10 K. Indirect exchange is suggested to be responsible for the spin-spin interaction, supported by RKKY interaction in the case of M tubes. For SC tubes, the spin-lattice relaxation via an Orbach process is suggested to determine the linewidth.
    Physical review. B, Condensed matter 07/2012; 86(4). · 3.77 Impact Factor
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    ABSTRACT: The ESR response from highly metal-semiconductor(M-SC) separated SWCNTs for temperatures T between 0.39 and 200 K is characteristically different for the two systems. The signal originates from defect spins but interaction with free electrons leads to a larger line width for M tubes. The latter decreases with increasing T whereas it increases with T for SC tubes. The spins undergo a ferromagnetic phase transition below around 10 K. Indirect exchange is suggested to be responsible for the spin-spin interaction, supported by RKKY interaction in the case of M tubes. For SC tubes spin-lattice relaxation via an Orbach process is suggested to determine the line width.
    06/2012;

Publication Stats

2k Citations
491.80 Total Impact Points

Institutions

  • 1990–2014
    • Princeton University
      • Department of Electrical Engineering
      Princeton, New Jersey, United States
  • 2005–2013
    • University of Oxford
      • Department of Materials
      Oxford, ENG, United Kingdom
    • Lawrence Berkeley National Laboratory
      • Materials Sciences Division
      Berkeley, California, United States
  • 2008–2011
    • University of California, Berkeley
      • Department of Electrical Engineering and Computer Sciences
      Berkeley, MO, United States
  • 2004
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States