22/10/15 14:00H Talk @ UFRJ – Olivier Buisson – Institut Néel – Grenoble, FrancePosted: October 15, 2015
Title: V-shape superconducting artificial atom for a novel quantum non demolition measurement
We present an experimental study on two superconducting qubits coupled via a large inductance . The resulting circuit exhibits a symmetric and an antisymmetric oscillation  which we use as a transmon and ancilla qubit, respectively. We observe a cross-anharmonicity between the two oscillations which is explained by the Josephson nonlinearity . This coupling leads the artificial atom to a have V-shape energy diagram.
We have predicted that such V-shape artificial atom, inside a circuit cavity quantum electrodynamics architecture, allows to read out the transmon qubit state by using the ancilla qubit frequency . In comparison with the most widely employed readout scheme for superconducting qubits, the dispersive readout, our approach promises a quantum non-demolition measurement with a significantly stronger measurement signal and without suffering from Purcell effect. In a measurement chain based on a state-of-the-art Josephson parametric amplifier, we predict a QND fidelity of up to 99.9% for a measurement time down to 60 ns . This should allow the measurement of quantum trajectories and the testing of some new concepts of quantum thermodynamics.
 É. Dumur, et al, “A V-shape superconducting artificial atom based on two inductively coupled transmons”, Phys. Rev. B 92, 020515 (2015).
 F. Lecocq, et al, “Coherent Frequency Conversion in a Superconducting Artificial Atom with Two Internal Degrees of Freedom”, Physical Review Letters 108, 107001 (2012).
 I. Diniz, et al, “Ultrafast quantum nondemolition measurements based on a diamond shaped artificial atom”, Physical Review A 87, 033837 (2013).
UFRJ- Centro de Tecnologia do Fundão, Bloco A, sala 343
Observação: Este será a segunda apresentação de Olivier na semana, essa vez o formato será o de um seminário normal com uma duracão de aprox. 50 mins.