Strain Tuning of Individual Atomic Tunneling Systems Detected by a Superconducting Qubit

Science  12 Oct 2012:
Vol. 338, Issue 6104, pp. 232-234
DOI: 10.1126/science.1226487

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Bend to Straighten

At low temperatures, the behavior of disordered solids, such as glasses, deviates from that of ordered crystals. The deviations may stem from the ability of some atomic entities to tunnel between two sites of almost identical energy, forming two low-energy states; such two-level systems (TLSs) are also thought to be a major contributor to the decoherence of superconducting qubits. Grabovskij et al. (p. 232) used mechanical strain to control the splitting between the energy levels of TLSs formed in the disordered barrier of the Josephson junction in a superconducting qubit. For some of the detected TLSs, the splitting exhibited the predicted minimum as a function of strain, verifying the TLS model of disordered solids.


In structurally disordered solids, some atoms or small groups of atoms are able to quantum mechanically tunnel between two nearly equivalent sites. These atomic tunneling systems have been identified as the cause of various low-temperature anomalies of bulk glasses and as a source of decoherence of superconducting qubits where they are sparsely present in the disordered oxide barrier of Josephson junctions. We demonstrated experimentally that minute deformation of the oxide barrier changes the energies of the atomic tunneling systems, and we measured these changes by microwave spectroscopy of the superconducting qubit through coherent interactions between these two quantum systems. By measuring the dependence of the energy splitting of atomic tunneling states on external strain, we verify a central hypothesis of the two-level tunneling model for disordered solids.

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