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Backens, Stefan (author), Shnirman, Alexander (author), Makhlin, Yuriy (author), Gefen, Yuval (author), Mooij, J.E. (author), Schön, Gerd (author)We analyze the control of Majorana zero-energy states by mapping the fermionic system onto a chain of Ising spins. Although the topological protection is lost for the Ising system, the mapping provides additional insight into the nature of the quantum states. By controlling the local magnetic field, one can separate the Ising chain into...journal article 2017
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Forn Diaz, P. (author), Romero, G. (author), Harmans, C.J.P.M. (author), Solano, E. (author), Mooij, J.E. (author)Understanding the interaction between light and matter is very relevant for fundamental studies of quantum electrodynamics and for the development of quantum technologies. The quantum Rabi model captures the physics of a single atom interacting with a single photon at all regimes of coupling strength. We report the spectroscopic observation...journal article 2016
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Mooij, J.E. (author), Schön, G. (author), Shnirman, A. (author), Fuse, T. (author), Harmans, C.J.P.M. (author), Rotzinger, H. (author), Verbruggen, A.H. (author)Superconducting nanowires are the dual elements to Josephson junctions, with quantum phase-slip (QPS) processes replacing the tunneling of Cooper pairs. When the QPS amplitude ES is much smaller than the inductive energy EL, the nanowire responds as a superconducting inductor. When the inductive energy is small, the response is capacitive. The...journal article 2015
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De Groot, P.C. (author), Ashhab, S. (author), Lupascu, A. (author), DiCarlo, L. (author), Nori, F. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We present a theoretical analysis of the selective darkening method for implementing quantum controlled-NOT (CNOT) gates. This method, which we have recently proposed and demonstrated, consists of driving two transversely coupled quantum bits (qubits) with a driving field that is resonant with one of the two qubits. For specific relative...journal article 2012
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Fedorov, A. (author), Macha, P. (author), Feofanov, A.K. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)The boundary between the classical and quantum worlds has been intensely studied. It remains fascinating to explore how far the quantum concept can reach with use of specially fabricated elements. Here we employ a tunable flux qubit with basis states having persistent currents of 1???A carried by a million pairs of electrons. By tuning the...journal article 2011
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Forn-Díaz, P. (author), Lisenfeld, J. (author), Marcos, D. (author), García-Ripoll, J.J. (author), Solano, E. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We measure the dispersive energy-level shift of an LC resonator magnetically coupled to a superconducting qubit, which clearly shows that our system operates in the ultrastrong coupling regime. The large mutual kinetic inductance provides a coupling energy of ?0.82??GHz, requiring the addition of counter-rotating-wave terms in the description of...journal article 2010
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Fedorov, A. (author), Feofanov, A.K. (author), Macha, P. (author), Forn-Díaz, P. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)A flux qubit biased at its symmetry point shows a minimum in the energy splitting (the gap), providing protection against flux noise. We have fabricated a qubit of which the gap can be tuned fast and have coupled this qubit strongly to an LC oscillator. We show full spectroscopy of the qubit-oscillator system and generate vacuum Rabi...journal article 2010
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Picot, T. (author), Schouten, R. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)Quantum state detectors based on switching of hysteretic Josephson junctions biased close to their critical current are simple to use but have strong backaction. We show that the backaction of a dc-switching detector can be considerably reduced by limiting the switching voltage and using a fast cryogenic amplifier, such that a single readout can...journal article 2010
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De Groot, P.C. (author), Van Loo, A.F. (author), Lisenfeld, J. (author), Schouten, R.N. (author), Lupa?cu, A. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We present experimental results on the crosstalk between two ac-operated dispersive bifurcation detectors, implemented in a circuit for high-fidelity readout of two strongly coupled flux qubits. Both phase-dependent and phase-independent contributions to the crosstalk are analyzed. For proper tuning of the phase the measured crosstalk is 0.1%...journal article 2010
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Lupa?cu, A. (author), Bertet, P. (author), Driessen, E.F.C. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We observed the dynamics of a superconducting flux qubit coupled to an extrinsic quantum system (EQS). The presence of the EQS is revealed by an anticrossing in the spectroscopy of the qubit. The excitation of a two-photon transition to the third excited state of the qubit-EQS system allows us to extract detailed information about the energy...journal article 2009
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Forn-Díaz, P. (author), Schouten, R.N. (author), Den Braver, W.A. (author), Mooij, J.E. (author), Harmans, C.J.P.M. (author)We fabricated and tested a squelch circuit consisting of a copper powder filter with an embedded Josephson junction connected to ground. For small signals (squelch ON), the small junction inductance attenuates strongly from dc to at least 1 GHz, while for higher frequencies dissipation in the copper powder increases the attenuation exponentially...journal article 2009
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Paauw, F.G. (author), Fedorov, A. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We experimentally demonstrate the in situ tunability of the minimum energy splitting (gap) of a superconducting flux qubit by means of an additional flux loop. Pulses applied via a local control line allow us to tune the gap over a range of several GHz on a nanosecond time scale. The strong flux sensitivity of the gap (up to ~0:7 GHz/m?0) opens...journal article 2009
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Picot, T. (author), Lupa?cu, A. (author), Saito, S. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)We analyze the relaxation of a superconducting flux qubit during measurement. The qubit state is measured with a nonlinear oscillator driven across the threshold of bifurcation, acting as a switching dispersive detector. This readout scheme is of quantum nondemolition type. Two successive readouts are used to analyze the evolution of the qubit...journal article 2008
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Ashhab, S. (author), Niskanen, A.O. (author), Harrabi, K. (author), Nakamura, Y. (author), Picot, T. (author), De Groot, P.C. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author), Nori, F. (author)We consider a system composed of two qubits and a high excitation energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well known results concerning the leading term in the...journal article 2008
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- Mooij, J.E. (author) patent 2007
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Eroms, J. (author), Van Schaarenburg, L.C. (author), Driessen, E.F.C. (author), Plantenberg, J.H. (author), Huizinga, C.M. (author), Schouten, R.N. (author), Verbruggen, A.H. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author)The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1?K and saturates below 0.8?K....journal article 2006
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- Lupescu, A. (author), Driessen, E.F.C. (author), Roschier, L. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author) journal article 2006
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- Bertet, P. (author), Harmans, C.J.P.M. (author), Mooij, J.E. (author) journal article 2006
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Kouwenhoven, L. (author), Mooij, J.E. (author)e present an excerpt of the document “Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe”, which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European...journal article 2005
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- Mooij, J.E. (author), Harmans, C.J.P.M. (author) journal article 2005