Aluminum hard mask technique for the fabrication of high quality submicron Nb/Al–AlOx/Nb Josephson junctions

Kaiser, Christoph; Meckbach, J.M.; Ilin, K.; Lisenfeld, Jürgen; Schäfer, Roland; Ustinov, A. V.; Siegel, M.

doi:10.1088/0953-2048/24/3/035005

Cited by 15 publications

(12 citation statements)

References 25 publications

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“…There are two experimental reported results, one for a single phase qubit of T 2 B21 ns (ref. 26), and another for a flux qubit of T 2 B500 ns (ref. 33).…”

Section: Discussionmentioning

confidence: 99%

“…An implementation of open system QA has recently been reported in a programmable architecture of superconducting flux qubits [20][21][22][23] , and applied to relatively simple protein folding and number theory problems 24,25 . Although quantum tunnelling has already been demonstrated 23 , the decoherence time in this architecture can be three orders of magnitude faster than the computational timescale 23,26 , due in part to the constraints imposed by the scalable design. It is interesting to note that this decoherence is in the instantaneous energy eigenbasis (see below).…”

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confidence: 99%

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Experimental signature of programmable quantum annealing

et al. 2013

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Quantum annealing is a general strategy for solving difficult optimization problems with the aid of quantum adiabatic evolution. Both analytical and numerical evidence suggests that under idealized, closed system conditions, quantum annealing can outperform classical thermalization-based algorithms such as simulated annealing. Current engineered quantum annealing devices have a decoherence timescale which is orders of magnitude shorter than the adiabatic evolution time. Do they effectively perform classical thermalization when coupled to a decohering thermal environment? Here we present an experimental signature which is consistent with quantum annealing, and at the same time inconsistent with classical thermalization. Our experiment uses groups of eight superconducting flux qubits with programmable spin-spin couplings, embedded on a commercially available chip with 4100 functional qubits. This suggests that programmable quantum devices, scalable with current superconducting technology, implement quantum annealing with a surprising robustness against noise and imperfections.

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“…There are two experimental reported results, one for a single phase qubit of T 2 B21 ns (ref. 26), and another for a flux qubit of T 2 B500 ns (ref. 33).…”

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Experimental signature of programmable quantum annealing

et al. 2013

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“…Nb is compatible with industrial level processing [19], its chemical stability yields lower wet etch rates and better etch selectivity towards oxides [12]. Nb is also used to fabricate wafer-scale trilayer Josephson junctions [13]- [15], making it an attractive candidate for large-scale superconducting device integration. Despite favorable physical and electrical properties, Nb forms 5-7 nm of native oxide, consisting of three components: NbO, NbO2, Nb2O5 [20], [21].…”

Section: Introductionmentioning

confidence: 99%

Investigation of Microwave Loss Induced by Oxide Regrowth in High- Q Niobium Resonators

et al. 2021

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The coherence of state-of-the-art superconducting qubit devices is predominantly limited by two-level-system defects, found primarily at amorphous interface layers. Reducing microwave loss from these interfaces by proper surface treatments is key to push the device performance forward. Here, we study niobium resonators after removing the native oxides with a hydrofluoric acid etch. We investigate the reappearance of microwave losses introduced by surface oxides that grow after exposure to the ambient environment. We find that losses in quantum devices are reduced by an order of magnitude, with internal Qfactors reaching up to 7×10 6 in the single photon regime, when devices are exposed to ambient conditions for 16 min. Furthermore, we observe that Nb2O5 is the only surface oxide that grows significantly within the first 200 hours, following the extended Cabrera-Mott growth model. In this time, microwave losses scale linearly with the Nb2O5 thickness, with an extracted loss tangent tanδNb2O5 = 9.9×10 -3 . Our findings are of particular interest for devices spanning from superconducting qubits, quantum-limited amplifiers, microwave kinetic inductance detectors to single photon detectors.

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“…For such flux qubits, the T 2 time can at present range from tens of nanoseconds to a few hundred nanoseconds [21,22], yet the computation lasts on the order of microseconds to milliseconds. If the qubits have all decohered long before the computation is over, how can this be reconciled with evidence that the D-Wave devices perform quantum annealing [23][24][25][26][27][28][29][30][31][32]?…”

Section: Introductionmentioning

confidence: 99%

Decoherence in adiabatic quantum computation

2015

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Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time-scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit T2 time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary cancellation methods, designed to improve the fidelity of adiabatic quantum computing in the closed system setting, remain beneficial in the open system setting. To address the high computational cost of master equation simulations, we also demonstrate that a quantum Monte Carlo algorithm that explicitly accounts for a thermal bosonic bath can be used to interpolate between classical and quantum annealing. Our study highlights and clarifies the significantly different role played by decoherence in the adiabatic and circuit models of quantum computing.

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Aluminum hard mask technique for the fabrication of high quality submicron Nb/Al–AlO_x/Nb Josephson junctions

Cited by 15 publications

References 25 publications

Experimental signature of programmable quantum annealing

Experimental signature of programmable quantum annealing

Investigation of Microwave Loss Induced by Oxide Regrowth in High- Q Niobium Resonators

Decoherence in adiabatic quantum computation

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