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. 2021 Mar 19;12(1):1779.
doi: 10.1038/s41467-021-22030-5.

New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds

Alexander P M Place #  1 , Lila V H Rodgers #  1 , Pranav Mundada  1 , Basil M Smitham  1 , Mattias Fitzpatrick  1 , Zhaoqi Leng  2 , Anjali Premkumar  1 , Jacob Bryon  1 , Andrei Vrajitoarea  1 , Sara Sussman  2 , Guangming Cheng  3 , Trisha Madhavan  1 , Harshvardhan K Babla  1 , Xuan Hoang Le  1 , Youqi Gang  1 , Berthold Jäck  2 , András Gyenis  1 , Nan Yao  3 , Robert J Cava  4 , Nathalie P de Leon  1 , Andrew A Houck  5
Affiliations

New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds

Alexander P M Place et al. Nat Commun. .

Abstract

The superconducting transmon qubit is a leading platform for quantum computing and quantum science. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that relaxation likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of two-dimensional transmon qubits have remained elusive for several years. Here, we fabricate two-dimensional transmon qubits that have both lifetimes and coherence times with dynamical decoupling exceeding 0.3 milliseconds by replacing niobium with tantalum in the device. We have observed increased lifetimes for seventeen devices, indicating that these material improvements are robust, paving the way for higher gate fidelities in multi-qubit processors.

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Conflict of interest statement

A.P.M.P., L.V.H.R., B.M.S., M.F., S.S., R.J.C., N.P.d.L., and A.A.H. filed for a provisional patent (62/933,758) that relates to this work. The other authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Tantalum-based transmon superconducting qubit.
a False-colored optical microscope image of a transmon qubit. The transmon consists of a Josephson junction shunted by two large capacitor islands made of tantalum (blue) on sapphire (gray). b Device layout image and corresponding circuit diagram of the transmon qubit coupled to the resonator via a coupling capacitor. c T1 measurement of Device 18, showing the excited state population Pe as a function of delay time Δt. Line represents a single exponential fit with a characteristic T1 time of 0.36 ± 0.01 ms. d Four-probe resistance measurement of the tantalum film showing Tc = 4.38 ± 0.02 K, consistent with the critical temperature of α-tantalum.
Fig. 2
Fig. 2. Lifetime and decoherence measurements.
a Lifetime (T1) and coherence time with dynamical decoupling (T2,CPMG) of Device 18 over time. b Summary of T1 time series measurements of all devices fabricated with a wet etch and piranha cleaning steps. Details about the specific processing steps for each device are given in Supplementary Table 1 and “Methods.” The yellow line shows the median, while the box spans the middle two quartiles of the data. The whiskers show the extremal measurements. Data for Devices 13, 14, and 17 are the average of 19, 14, and 7 individual T1 measurements, respectively, while the rest are the average of at least 32 measurements. Each device was measured over a period of hours to days, and Devices 11 and 13 include data from multiple dilution refrigerator cycles. c T2,Echo measurement of Device 18, showing the excited state population Pe as a function of delay time Δt. Solid blue line shows a stretched exponential fit to the data. The fit gives T2,Echo = 249 ± 4 μs. d T2,CPMG of Device 11 as a function of the number of gates in a CPMG pulse sequence. The error bars denote one standard deviation in the data.
Fig. 3
Fig. 3. Microscopy and spectroscopy of tantalum films.
a STEM image of the tantalum film, showing single-crystal columns with the growth direction oriented along the [110] axis. b Atomic-resolution STEM image of an interface between two columns, viewed from 11¯1 and 001 zone axes, respectively. Fourier transforms (insets) of the image show that the columns are oriented with the image plane perpendicular to the 111 or 100 directions. c STEM image of a horizontal device cross section, showing grain boundaries. Image contrast at grain boundaries results from diffraction contrast caused by interfacial defects. d XPS spectrum of a device, exhibiting peaks from tantalum metal and Ta2O5. Other oxidation states of tantalum are expected to have binding energies between 22.2 and 23.8 eV, . e High-resolution STEM with integrated differential phase contrast imaging of the interface between the sapphire and tantalum showing epitaxial growth.
See this image and copyright information in PMC

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