Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 29: Quantenkoh
ärenz und Quanteninformationssysteme II

TT 29.8: Talk

Thursday, March 11, 2004, 16:30–16:45, H19

Enhancing the Gate Performance of Superconducting Qubits by DFS Encoding — •Markus J. Storcz¹, Frank K. Wilhelm¹, Jiri Vala², Kenneth R. Brown², Julia Kempe², and K. Birgitta Whaley² — ¹Sektion Physik und CeNS, Ludwig-Maximilians-Universität, Theresienstr. 37, 80333 München — ²Department of Chemistry and Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720

Solid state qubits such as superconducting qubits are potentially extremely scalable. However, strong decoherence may be caused or transferred to the qubits by various elements of the circuit that couples individual qubits, in particular when couplings over long physical distance are implemented. We propose encoding into a subspace protected against collective phase errors for a chain of superconducting qubits that are coupled to nearest neighbors with σ_x⁽ⁱ⁾ σ_x⁽ⁱ⁺¹⁾ + σ_y⁽ⁱ⁾ σ_y⁽ⁱ⁺¹⁾-type of interaction. We show by numerical simulation of the encoded operations for an ohmic environment that, even if the mathematical preconditions for full DFS-protection are not fully satisfied, the encoding results in significant improvement of the gate performance on the logical qubits at low temperatures. Moreover, for a super-ohmic environment perfect protection and gate performance of the logical qubits can be achieved.