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Tuned transition from quantum to classical for macroscopic quantum states
A. Fedorov, P. Macha, A. K. Feofanov +2
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 fabr…
Selective darkening of degenerate transitions demonstrated with two superconducting quantum bits
P. C. de Groot, J. Lisenfeld, R. N. Schouten +4
Controlled manipulation of quantum states is central to studying natural and artificial quantum systems. If a quantum system consists of interacting sub-units, the nature of the co…
Low-crosstalk bifurcation detectors for coupled flux qubits
P. C. de Groot, A. F. van Loo, J. Lisenfeld +4
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 couple…
QND measurement of a superconducting qubit in the weakly projective regime
T. Picot, R. Schouten, C. J. P. M. Harmans +1
Quantum state detectors based on switching of hysteretic Josephson junctions biased close to their critical current are simple to use but have strong back-action. We show that the…
Observation of the Bloch-Siegert Shift in a Qubit-Oscillator System in the Ultrastrong Coupling Regime
P. Forn-Díaz, J. Lisenfeld, D. Marcos +4
We measure the dispersive energy-level shift of an resonator magnetically coupled to a superconducting qubit, which clearly shows that our system operates in the ultrastrong c…
Strong Coupling of a Quantum Oscillator to a Flux Qubit at its Symmetry Point
A. Fedorov, A. K. Feofanov, P. Macha +3
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 whose gap can be tu…