Hydrogen bonds in Al(2)O(3) as dissipative two-level systems in superconducting qubits

Dissipative two-level systems (TLS) have been a long-standing problem in glassy solids over the last fifty years, and have recently gained new relevance as sources of decoherence in quantum computing. Resonant absorption by TLSs in the dielectric poses a serious limitation to the performance of superconducting qubits; however, the microscopic nature of these systems has yet to be established. Based on first-principles calculations, we propose that hydrogen impurities in Al(2)O(3) are the main source of TLS resonant absorption. Hydrogen is an ubiquitous impurity and can easily incorporate in Al(2)O(3). We find that interstitial H in Al(2)O(3) forms a hydrogen bond (O-H…O). At specific O-O distances, consistent with bond lengths found in amorphous Al(2)O(3) or near Al(2)O(3) surfaces or interfaces, the H atom feels a double well. Tunneling between two symmetric positions gives rise to resonant absorption in the range of 10 GHz, explaining the experimental observations. We also calculate the expected qubit-TLS coupling and find it to lie between 16 and 20 MHz, consistent with experimental measurements.