Institut Néel Grenoble

• Personnel
• Recherche
  • Superconducting Quantum Circuits
    • vide
    • Superconducting Phase Qubit
    • Tunable coupling coupling between a charge qubit and a phase qubit
    • Topological protected qubit
      • Noise and Decoherence
      • Protection mechanism
      • Current-phase relation of a rhombi chain
  • QSPINMOTION : coherent transport of a single flying electron spin
  • FLYELEC : Quantum optics with flying electrons
  • SUPERNEMS : Nanomechanics using superconducting diamonds
  • Graphene
  • SEMITOPO : Strained HgTe, a 3D topological insulator
  • MESOGLASS : probing spin glass with mesoscopic physics
  • FREQJO : FREquency-to-CUrrent conversion in JOsephson Crystals
  • GEOMDISS : a topological quantum pump
• Techniques
• Formation
• Publications
• Collaborations
• Travailler avec nous

We would like to realize a novel class of topologically protected quantum bits (qubits) with much longer coherence time and therefore smaller error rate that would allow for real application of JJ circuits for quantum information processing. This would overcome the major barrier for the quantum computer implementation in JJ circuits : the fact that the error rate of all existing superconducting qubits is far too high in order to implement scalable quantum computations. Read more

The physical system we study are circuits based on rhombi chains, a rhombus being a superconducting loop with four identical JJs (see Figure 1). These circuits allow to realise the general idea of a topologically protected qubit proposed by Kitaev[1,2,3,4]. Read more

 

We have measured the ground state energy of a rhombi chain in the classical and quantum regime as a function of bias phase difference over the chain [6]. The ground state of the chain can be determined by a measurement of the chain’s current-phase relation I() : the supercurrent is given by the derivative of E₀() with respect to . In order to measure the current-phase relation of a rhombi chain, we implemented an escape measurement using a large JJ which is connected in parallel to the chain (Fig. 1). Read more

 

 Fig. 1 : a) SEM image of a rhombi chain (N = 8) in the closed superconducting circuit. b) Shunt junction. c) Single rhombus. d) Schematic of the circuit designed to measure the current-phase relation of a rhombi chain. e) At half flux frustration the classical eigenstates of a single rhombus are given by the clockwise and anticlockwise circulating currents.

 

Current research :

We are currently working on the experimental identification of the energy spectrum of circuits based on rhombi and SQUID chains.

 

Current PhD : Ioan Pop

 

Contact : Bernard Pannetier and Wiebke Guichard

 

Collaborations :

 

Lev Ioffe, Michael Gershenson, Rutgers University, New Jersey

Bénoit Douçot, LPTHE-CNRS, Paris

 

 

References :

 

[1] A. Kitaev, quant-ph/9707021, Annales Phys. 303 (2003) 2-30

[2] L. Ioffe et al., Nature, 415, 503, (2002)

[3] B. Douçot and J. Vidal, Phys. Rev. Lett. 88, 227005 (2002)

[4] S. Gladchenko et al, Nature Physics 5, No 1 (2008)

[5] I. Protopopov et al. Phys. Rev. B 70, 184519, (2004)

[6] I. Pop et al., Phys. Rev. B 78, 104504 (2008)

[7] K.A. Matveev et al., Phys. Rev. Lett. 89, 096802 (2002)

 

 

Funding

 

MIDAS ( European Strep ”Macroscopic Interference Devices on Atoms and Solids”)