Jeremy Levy | University of Pittsburgh (original) (raw)

Papers by Jeremy Levy

Applied Physics A-materials Science & Processing, 2004

We report a method for producing BST films with consistently high figures of merit for tunable mi... more We report a method for producing BST films with consistently high figures of merit for tunable microwave applications. (Ba1-x,Srx)TiO3 (x=0.4, target doped with 1% W) thin films have been deposited using pulsed laser deposition onto (100)MgO substrates. Films were deposited at low partial pressures of oxygen (50 mTorr) at a substrate temperature of 730 °C. An analysis of the X-ray diffraction data indicates that the film has a nearly cubic structure, with the overall lattice parameter enlarged relative to the bulk material due to the presence of oxygen vacancies. A post-deposition anneal of the film in flowing oxygen (1000 °C for 6 h) resulted in a decrease in the lattice parameter while remaining nearly cubic. An analysis of the microwave dielectric properties (1–20 GHz) showed that the annealed film exhibited about 10% tunability for an applied bias field of 67 kV/cm with a dielectric Q(1/tanδ)>600. Investigation of the films by time-resolved confocal scanning optical microscopy (CSOM) has revealed that there is an out-of-plane polarization at zero applied field (EDC=0). The results show that the paraelectric response is relatively insensitive to applied field, while the ferroelectric response is correlated with the growth of in-plane nanodomains. We find these results to be consistent with a large number of studies that show that strain-relief is of paramount importance if ferroelectric films are to be developed as microwave circuit components.

Physical Review Letters, 2000

The microwave dielectric response of a ferroelectric thin film is measured locally using time-res... more The microwave dielectric response of a ferroelectric thin film is measured locally using time-resolved confocal scanning optical microscopy. Measurements performed on an ensemble of nanometer-scale regions show a well-defined phase shift between the paraelectric and ferroelectric response at 2-4 GHz. Application of a static electric field produces large local variations in the phase of the ferroelectric response. These variations are attributed to the growth of in-plane ferroelectric nanodomains whose size-dependent relaxation frequencies lead to strong dielectric dispersion at mesoscopic scales.

Science, 2009

Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, hav... more Metal oxide semiconductor field-effect transistors, formed using silicon dioxide and silicon, have undergone four decades of staggering technological advancement. With fundamental limits to this technology close at hand, alternatives to silicon dioxide are being pursued to enable new functionality and device architectures. We achieved ferroelectric functionality in intimate contact with silicon by growing coherently strained strontium titanate (SrTiO3) films via oxide molecular beam epitaxy in direct contact with silicon, with no interfacial silicon dioxide. We observed ferroelectricity in these ultrathin SrTiO3 layers by means of piezoresponse force microscopy. Stable ferroelectric nanodomains created in SrTiO3 were observed at temperatures as high as 400 kelvin.

Applied Physics Letters, 1997

An optical technique based on confocal scanning optical microscopy (CSOM) is used to image the fe... more An optical technique based on confocal scanning optical microscopy (CSOM) is used to image the ferroelectric polarization of BaxSr1-xTiO3 (BST) thin films at room temperature with submicron spatial resolution. BST films were grown by pulsed laser deposition on (100) SrTiO3 and MgO substrates at 750 °C in 300 mTorr of oxygen and postdeposition annealed in flowing oxygen at temperatures ⩽1250 °C. Films of both paraelectric (x=0.5) and ferroelectric (x=0.8) compositions show a coexistence of both paraelectric and ferroelectric phases. The ferroelectric regions exhibit polarization switching and hysteresis at relatively low (1-2 kV/cm) applied fields. These results suggest that nonuniform stress is responsible for the strong inhomogeneous thermal broadening of the ferroelectric phase transition, and that dielectric loss in thin films may be dominated by a relatively small fraction of nanometer-sized regions.

Physical Review B, 2006

... AD Bruce and RA Cowley, J. Phys. C 6, 2422 (1973) [INSPEC][ADS][CAS]. ... Y. Barad and V. Gop... more ... AD Bruce and RA Cowley, J. Phys. C 6, 2422 (1973) [INSPEC][ADS][CAS]. ... Y. Barad and V. Gopalan, Integr. Ferroelectr. 44, 19 (2002). A. Vasudevarao, A. Kumar, L. Tian, JH Haeni, YL Li, DG Schlom, LQ Chen, QX Jia, and Venkatraman Gopalan (unpublished, 2006). ...

Integrated Ferroelectrics, 1998

Ferroelectric thin films, deposited by pulsed laser deposition (PLD), are currently being used to... more Ferroelectric thin films, deposited by pulsed laser deposition (PLD), are currently being used to develop a new class of tunable microwave circuits based on the electric field dependence of the dielectric constant. Single phase, (100) oriented Ba0.5Sr0.5TiO3 (BST) films have been deposited onto (100) LaAlO3, SrTiO3, and MgO substrates. Interdigitated capacitors patterned on top of the ferroelectric film have been

Nature, 2004

Supplementary Information accompanies the paper on www.nature.com/nature. Acknowledgements We are... more Supplementary Information accompanies the paper on www.nature.com/nature. Acknowledgements We are indebted to the Cluster team for the design and successful operation of the Cluster II mission.

Physical Review Letters, 2002

An efficient and intuitive framework for universal quantum computation is presented that uses pai... more An efficient and intuitive framework for universal quantum computation is presented that uses pairs of spin-1/2 particles to form logical qubits and a single physical interaction, Heisenberg exchange, to produce all gate operations. Only two Heisenberg gate operations are required to produce a controlled pi-phase shift, compared to 19 for exchange-only proposals employing three spins. Evolved from well-studied decoherence-free subspaces, this architecture inherits immunity from collective decoherence mechanisms. The simplicity and adaptability of this approach should make it attractive for spin-based quantum computing architectures.

Science, 2003

We present a scheme that enables gigahertz-bandwidth three-dimensional control of electron spins ... more We present a scheme that enables gigahertz-bandwidth three-dimensional control of electron spins in a semiconductor heterostructure with the use of a single voltage signal. Microwave modulation of the Landé g tensor produces frequency-modulated electron spin precession. Driving at the Larmor frequency results in g-tensor modulation resonance, which is functionally equivalent to electron spin resonance but without the use of time-dependent magnetic fields. These results provide proof of the concept that quantum spin information can be locally manipulated with the use of high-speed electrical circuits.

Physical Review B, 1996

... N. Samarth Department of Physics, The Pennsylvania State University, University Park, Pennsyl... more ... N. Samarth Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802 V. Nikitin, PA Crowell, J. Shi, J. Levy ... Simultaneous measurements of the intensity of the specular beam show a sudden damping on RHEED oscillations at the 2D-3D ...

Physical Review Letters, 1995

... PHYSICAL REVIEW LETTERS Enhanced Spin Interactions in Digital Magnetic Heterostructures SA Cr... more ... PHYSICAL REVIEW LETTERS Enhanced Spin Interactions in Digital Magnetic Heterostructures SA Crooker, DA Tulchinsky, J. Levy, and DD Awschalom Department of Physics, University of California, Santa Barbara, California 93106 R. Garcia and N. Samarth Department of ...

Physical Review Letters, 1996

Interest in the spin degrees of freedom of mesoscopic electronic systems has fueled a need to fin... more Interest in the spin degrees of freedom of mesoscopic electronic systems has fueled a need to find new methods of probing them. The effects of interfaces, disorder, and local magnetic interactions strongly influence the transfer of spin angular momentum in small geometries, yet many of the underlying physical mechanisms are poorly understood. In recent years, magnetic semiconductor quantum wells, with

Physical Review A, 2005

A class of architectures is advanced for cluster state quantum computation using quantum dots. Th... more A class of architectures is advanced for cluster state quantum computation using quantum dots. These architectures include using single and multiple dots as logical qubits. Special attention is given to the supercoherent qubits introduced by Bacon, Brown, and Whaley [Phys. Rev. Lett. {\bf 87}, 247902 (2001)] for which we discuss the effects of various errors, and present means of error protection.

Physical Review B, 2003

We show that a wide range of spin clusters with antiferromagnetic intracluster exchange interacti... more We show that a wide range of spin clusters with antiferromagnetic intracluster exchange interaction allows one to define a qubit. For these spin cluster qubits, initialization, quantum gate operation, and readout are possible using the same techniques as for single spins. Quantum gate operation for the spin cluster qubit does not require control over the intracluster exchange interaction. Electric and magnetic fields necessary to effect quantum gates need only be controlled on the length scale of the spin cluster rather than the scale for a single spin. Here, we calculate the energy gap separating the logical qubit states from the next excited state and the matrix elements which determine quantum gate operation times. We discuss spin cluster qubits formed by one- and two-dimensional arrays of s=1/2 spins as well as clusters formed by spins s>1/2. We illustrate the advantages of spin cluster qubits for various suggested implementations of spin qubits and analyze the scaling of decoherence time with spin cluster size.

Physical Review Letters, 2003

We study the low energy states of finite spin chains with isotropic (Heisenberg) and anisotropic ... more We study the low energy states of finite spin chains with isotropic (Heisenberg) and anisotropic (XY and Ising-like) exchange interaction with uniform and non-uniform coupling constants. We show that for an odd number of sites a spin cluster qubit can be defined in terms of the ground state doublet. This qubit is remarkably insensitive to the placement and coupling anisotropy of spins within the cluster. One- and two-qubit quantum gates can be generated by magnetic fields and inter-cluster exchange, and leakage during quantum gate operation is small. Spin cluster qubits inherit the long decoherence times and short gate operation times of single spins. Control of single spins is hence not necessary for the realization of universal quantum gates.