E. Il’ichev

Publications (10)14.42 Total impact

• Source

  Available from: A. N. Omelyanchouk

  Article: Multiphoton excitations and inverse population in a system of two flux qubits

  E. Il’ichev, S. N. Shevchenko, S. H. W. van der Ploeg, M. Grajcar, E. A. Temchenko, A. N. Omelyanchouk, H.-G. Meyer
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  ABSTRACT: We study the multiphoton spectroscopy of artificial solid-state four-level quantum system. This system is formed by two coupled superconducting flux qubits. When multiple driving frequency of the applied microwaves matches the energy difference between any two levels, the transition to the upper level is induced. We demonstrate two types of the multiphoton transitions: direct transitions between two levels and ladder-type transitions via an intermediate level. Our calculations show, that for the latter transitions, in particular, the inverse population of the excited state with respect to the ground one is realized. These processes can be useful for the control of the level population for the multilevel scalable quantum systems.
  Phys. Rev. B. 08/2009; 81(1).
• Article: Weak continuous measurements of multiqubits systems

  E. Il’ichev, S. H. W. van der Ploeg, M. Grajcar, H.-G. Meyer
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  ABSTRACT: In this review we summarize our recent experiments on the investigation on superconducting qubits. Instead of strong projective measurement used by other groups in their first pioneering experiments we have proposed and realized a weak continuous readout which belongs to the class of quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at the so called sweet (or magic) point where a qubit is in a superposition of two classical states and its sensitivity to external noise is minimized. In this scheme, which is widely used nowadays, the superconducting oscillator coupled to superconducting qubit is used as a detector of the qubit’s state. Such system is analogue to a system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics in artificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused by energy exchange between an oscillator and a flux qubit. Using the Sisyphus effect we show consistency between the adiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us to characterize the more complicated system of coupled qubits by making use of the same method. We have realized and studied fixed ferromagnetic, antiferromagnetic as well as tunable qubit–qubit coupling. We argue that ground state measurements can be used for characterization of entangled states in coupled flux qubits.
  Quantum Information Processing 05/2009; 8(2):133-153. · 2.00 Impact Factor
• Source

  Available from: Alexandre Zagoskin

  Article: A Characterization of Global Entanglement

  Peter J. Love, Alec Maassen van den Brink, A. Yu. Smirnov, M. H. S. Amin, M. Grajcar, E. Il’ichev, A. Izmalkov, A. M. Zagoskin
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  ABSTRACT: We define a set of 2 n−1−1 entanglement monotones for n qubits and give a single measure of entanglement in terms of these. This measure is zero except on globally entangled (fully inseparable) states. This measure is compared to the Meyer–Wallach measure for two, three, and four qubits. We determine the four-qubit state, symmetric under exchange of qubit labels, which maximizes this measure. It is also shown how the elementary monotones may be computed as a function of observable quantities. We compute the magnitude of our measure for the ground state of the four-qubit superconducting experimental system investigated in [M. Grajcar etal., Phys. Rev. Lett. 96, 047006 (2006)], and thus confirm the presence of global entanglement in the ground state.
  Quantum Information Processing 05/2007; 6(3):187-195. · 2.00 Impact Factor
• Article: Paramagnetic effect in YBa_ {2} Cu_ {3} O_ {7-x} grain-boundary junctions

  E. Il’ichev, F. Tafuri, M. Grajcar, R. P. J. IJsselsteijn, J. Weber, F. Lombardi, J. R. Kirtley
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  ABSTRACT: A detailed investigation of the magnetic response of YBa2Cu3Ox grain-boundary Josephson junctions has been carried out using both radio-frequency measurements and scanning superconducting quantum interference device microscopy. In a nominally zero-field-cooled regime we observed a paramagnetic response at low external fields for 45° asymmetric grain boundaries. We argue that the observed phenomenology results from the d-wave order-parameter symmetry and depends on Andreev bound states.
  Phys. Rev. B. 07/2003; 68(1).
• Article: Microfabricated oscillator for radio-frequency microscopy with integrated magnetic field concentrator

  T. May, E. Il’ichev, H.-G. Meyer, M. Grajcar
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  ABSTRACT: We present a lithographically manufactured chip with niobium thin-film pancake coils, and a washerlike structure above this coil for focusing flux. Due to a wide range of coupling coefficients, various samples can be investigated in flip-chip or on-chip configuration, with the aim of evaluating the superconducting current-phase relation. With this, structures with dimensions in the order of 10 μm were coupled to the resonance circuit with coupling coefficients from 10−3 up to 0.9. Resonance frequencies in the 10 MHz range and quality factors of about 500 were obtained with external capacitors. Furthermore, the chip is designed to facilitate the manufacture of superconducting qubits in the center of the coil. This offers the possibility of combining on one chip novel technologies for fabricating superconducting qubits along with high-quality tank circuits for studying the qubits.© 2003 American Institute of Physics.
  Review of Scientific Instruments 02/2003; 74(3):1282-1284. · 1.37 Impact Factor
• Article: Radio-frequency based monitoring of small supercurrents

  E. Il’ichev, V. Zakosarenko, L. Fritzsch, R. Stolz, H. E. Hoenig, H.-G. Meyer, M. Götz, A. B. Zorin, V. V. Khanin, A. B. Pavolotsky, J. Niemeyer
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  ABSTRACT: We consider the applicability of the established rf readout technique, which allows to obtain the supercurrent-phase relation of a Josephson element from impedance measurements in the phase-biased regime. In experiments on Nb-based single and double tunnel junctions, we demonstrate that this method holds even if the Josephson coupling energy is smaller than the thermal energy. Compared with conventional current–voltage measurements, we evaluate the rf technique to be favorable in particular for investigations of small supercurrents in low-capacitance Josephson elements. © 2001 American Institute of Physics.
  Review of Scientific Instruments 02/2001; 72(3):1882-1887. · 1.37 Impact Factor
• Article: Harmonic current-phase relation in Nb–Al-based superconductor/insulator/normal conductor/insulator/superconductor-type Josephson junctions between 4.2 K and the critical temperature

  M. Götz, V. V. Khanin, H. Schulze, A. B. Zorin, J. Niemeyer, E. Il’ichev, A. Chwala, H. E. Hoenig, H.-G. Meyer
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  ABSTRACT: For a study of the supercurrent–phase relationship, we have fabricated Nb/Al/AlOx/Al/AlOx/Al/Nb-based Josephson junctions of low critical current density. At 4.2 K, junctions of a nominal area of 10×10 μm2 showed a nonhysteretic dc current–voltage characteristic with a critical current of about 10 μA. Similar junctions were part of washer-type rf superconductor quantum interference devices. These samples were inductively coupled to high-quality tank circuits for measurements at 4.2 K or at higher temperatures up to values close to the critical temperature of niobium. In this range, the current–phase relation, as deduced from impedance measurements of the phase-biased junction, did not deviate significantly from the sinusoidal shape. © 2000 American Institute of Physics.
  Applied Physics Letters 08/2000; 77(9):1354-1356. · 3.84 Impact Factor
• Article: Temperature dependence of the current-phase relation for YBa2Cu3O7−x step-edge Josephson junctions

  E. Il’ichev, V. Zakosarenko, V. Schultze, H.-G. Meyer, H. E. Hoenig, V. N. Glyantsev, A. Golubov
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  ABSTRACT: The current-phase relation (CPR) of YBa2Cu3O7−x step-edge Josephson junctions was investigated experimentally at various temperatures. The investigated junctions were incorporated into a washer-shaped superconducting ring with inductance L ∼ 300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency between 9 MHz and 40 MHz. The CPR was obtained from the measurement of the impedance of the phase-biased junction. At high temperatures and low critical current the experimentally observed CPR is sinusoidal. The same results were obtained at low temperatures when the rms flux noise in the ring is negligible. In the case of larger critical current and finite noise, deviations of the apparent CPR from sinusoidal dependence were found. The deviations can be described by thermal fluctuations of the magnetic flux in the ring. © 1998 American Institute of Physics.
  Applied Physics Letters 02/1998; 72(6):731-733. · 3.84 Impact Factor
• Chapter: The current-phase relation in HTS Josephson junctions

  E. Il’ichev, V. Zakosarenko, R. P. J. Ijsselsteijn, V. Schultze, H.-G. Meyer, H. E. Hoenig
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  ABSTRACT: The current-phase relation of YBa2Cu3O7−x step-edge as well as 24° and 45° grain boundary Josephson junctions has been investigated experimentally. The junctions were incorporated into a washer-shaped superconducting ring with inductance L≈80–300 pH. The ring was inductively coupled to a tank circuit with a resonance frequency 9…40 MHz. The current-phase relation was obtained from the measurement of the impedance of the phase-biased junction. It is shown, that experimentally observed deviations from harmonic behavior of the apparent current-phase relation for step-edge and 24° grain boundary junctions can be explained by the influence of thermal noise. The current-phase relation of 45° grain boundary junctions was found to be extremely non-harmonic. The reasons of this unusual behavior are discussed.
  01/1970: pages 507-519;
• Article: Phase dependence of the Josephson current in inhomogeneous high-T_ {c} grain-boundary junctions

  E. Il’ichev, V. Zakosarenko, R. P. J. IJsselsteijn, H. E. Hoenig, H.-G. Meyer, M. V. Fistul, P. Müller
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  ABSTRACT: We present an experimental and theoretical study of the current-phase relation Is(φ) for 45° grain boundaries in YBa2Cu3O7-x films. A model of strongly inhomogeneous Josephson junctions, in which the presence of randomly alternating current leads to a deviation of Is(φ) from the well-known sin(φ) dependence, has been used. This deviation decreases with the temperature T and is described by the formula Is(φ)=Ic(T)(sinφ+γ(T)sin2φ). Using the developed model, the coefficient γ is calculated and its temperature dependence is found to be in good agreement with experiment.
  Phys. Rev. B. 59(17).