Parity-Protected Josephson Qubits
Michael Gershenson
Department of Physics and Astronomy, Rutgers University, New Jersey
Tue, Jul. 12th 2016, 15:00-16:00
Bât. K, Salle R. Lemaire (K223), Institut Néel

ATTENTION : en raison de la mise en application avancée du plan Vigipirate, toutes les personnes qui ne possèdent pas de badge CNRS doivent nous signaler leur venue avant lundi 11 juillet 15h45, afin d’ajouter leur nom à la liste des personnes autorisées à entrer sur le site.


I will discuss two types of protected qubits that decouple logical states from the environment by encoding them in a parity of a large number.  The first type, the so-called charge-pairing qubit, represents a chain of two Josephson elements characterized by the π periodicity of the phase dependence of their Josephson energy E_J cos(2φ) (the so-called Josephson rhombi [1]).  The second type, the flux-pairing qubit, consists of a 4π periodic Josephson element (a Cooper pair box with the charge e on the central island) shunted by a superinductor [2].  The lowest-energy quantum states of the charge-pairing qubit are encoded in the parity of Cooper pairs on a superconducting island flanked by the Josephson rhombi. The flux-pairing qubit encodes its quantum states in the parity of magnetic flux quanta in a superconducting loop.  The design of these devices enforces, respectively, charge- and flux-pairing, prohibits the mixing of lowest-energy quantum states, and protects the qubits from both the decay and dephasing.  We have fabricated the prototypes of these qubits and studied the low-energy excitations in these devices [3,4]  For the charge-pairing devices, we observed a 100-fold increase of the decay time T1 (up to 100 s) in comparison with the unprotected state of the same qubit [3].


1.  S. Gladchenko, D. Olaya, E. Dupont-Ferrier, B. Douçot, L.B. Ioffe, and M.E. Gershenson. Superconducting Nanocircuits for Topologically Protected Qubits. Nature Physics 5, 48-53 (2009).

2.  M.T. Bell, I.A. Sadovskyy, L.B. Ioffe, A.Yu. Kitaev, and M.E. Gershenson. Quantum Superinductor with Tunable Non-Linearity. Phys. Rev. Lett. 109, 137003 (2012).

3.  M.T. Bell, J. Paramanandam, L.B. Ioffe, and M.E. Gershenson. Protected Josephson Rhombus Chains. Phys. Rev. Lett. 112, 167001 1-5 (2014).

4.  M.T. Bell, W. Zhang, L.B. Ioffe, and M.E. Gershenson. Spectroscopic Evidence of the Aharonov-Casher Effect in a Cooper Pair Box. Phys. Rev. Lett. 116, 107002 (2016).

Contact : Michel BENINI


Retour en haut