The Josephson effect describes the flow of supercurrent in a weak link—such as a tunnel junction, nanowire or molecule—between two superconductors1. It is the basis for a variety of circuits and devices, with applications ranging from medicine2 to quantum information3. Experiments using Josephson circuits that behave like artificial atoms4 are now revolutionizing the way we probe and exploit the laws of quantum physics5,6. Microscopically, the supercurrent is carried by Andreev pair states, which are localized at the weak link. These states come in doublets and have energies inside the superconducting gap7,8,9,10. Existing Josephson circuits are based on properties of just the ground state of each doublet, and so far the excited states have not been directly detected. Here we establish their existence through spectroscopic measurements of superconducting atomic contacts. The spectra, which depend on the atomic configuration and on the phase difference between the superconductors, are in complete agreement with theory. Andreev doublets could be exploited to encode information in novel types of superconducting qubits11,12,13.
This is a preview of subscription content
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Josephson, B. D. Possible new effects in superconductive tunnelling. Phys. Lett. 1, 251–253 (1962)
Busch, S. et al. Measurements of T1-relaxation in ex vivo prostate tissue at 132 μT. Magn. Reson. Med. 67, 1138–1145 (2012)
Erik Lucero et al. High-fidelity gates in a single Josephson qubit. Nature Phys. 8, 719–723 (2012)
Wendin, G. & Shumeiko, V. S. Quantum bits with Josephson junctions. Low Temp. Phys. 33, 724–744 (2007)
Fink, J. M. et al. Climbing the Jaynes–Cummings ladder and observing its nonlinearity in a cavity QED system. Nature 454, 315–318 (2008)
Hofheinz, M. et al. Synthesizing arbitrary quantum states in a superconducting resonator. Nature 459, 546–549 (2009)
Kulik, I. O. Macroscopic quantization and proximity effect in S-N-S junctions. Sov. Phys. JETP 30, 944–950 (1970)
Furusaki, A. & Tsukada, M. Dc Josephson effect and Andreev reflection. Solid State Commun. 78, 299–302 (1991)
Beenakker, C. W. J. & van Houten, H. Josephson current through a superconducting quantum point contact shorter than the coherence length. Phys. Rev. Lett. 66, 3056–3059 (1991)
Bagwell, P. F. Suppression of the Josephson current through a narrow, mesoscopic, semiconductor channel by a single impurity. Phys. Rev. B 46, 12573–12586 (1992)
Zazunov, A., Shumeiko, V. S., Bratus’, E. N., Lantz, J. & Wendin, G. Andreev level qubit. Phys. Rev. Lett. 90, 087003 (2003)
Chtchelkatchev, N. M. & Nazarov, V. Andreev quantum dots for spin manipulation. Phys. Rev. Lett. 90, 226806 (2003)
Padurariu, C. & Nazarov, V. Spin blockade qubit in a superconducting junction. Europhys. Lett. 100, 57006–57011 (2012)
Bardeen, J., Cooper, L. N. & Schrieffer, J. R. Theory of superconductivity. Phys. Rev. 108, 1175–1204 (1957)
Della Rocca, M. L. et al. Measurement of the current-phase relation of superconducting atomic contacts. Phys. Rev. Lett. 99, 127005 (2007)
Zgirski, M. et al. Evidence for long-lived quasiparticles trapped in superconducting point contacts. Phys. Rev. Lett. 106, 257003 (2011)
Deacon, R. S. et al. Tunneling spectroscopy of Andreev energy levels in a quantum dot coupled to a superconductor. Phys. Rev. Lett. 104, 076805 (2010)
Pillet, J.-D. et al. Andreev bound states in supercurrent-carrying carbon nanotubes revealed. Nature Phys. 6, 965–969 (2010)
Morpurgo, A. F., Baselmans, J. J. A., van Wees, B. J. & Klapwijk, T. M. Energy spectroscopy of the Josephson supercurrent. J. Low Temp. Phys. 118, 637–651 (2000)
Fuechsle, M. et al. Effect of microwaves on the current-phase relation of superconductor normal-metal superconductor Josephson junctions. Phys. Rev. Lett. 102, 127001 (2009)
van Ruitenbeek, J. M. et al. Adjustable nanofabricated atomic size contacts. Rev. Sci. Instrum. 67, 108–111 (1996)
Edstam, J. & Olsson, H. K. Josephson broadband spectroscopy to 1 THz. Appl. Phys. Lett. 64, 2733–2735 (1994)
Leppäkangas, J., Thuneberg, E., Lindell, R. & Hakonen, P. Tunneling of Cooper pairs across voltage-biased asymmetric single-Cooper-pair transistors. Phys. Rev. B 74, 054504 (2006)
Billangeon, P.-M., Pierre, F., Bouchiat, H. & Deblock, R. Very high frequency spectroscopy and tuning of a single-Cooper-pair transistor with an on-chip generator. Phys. Rev. Lett. 98, 126802 (2007)
Scheer, E., Joyez, P., Esteve, D., Urbina, C. & Devoret, M. H. Conduction channel transmissions of atomic-size aluminum contacts. Phys. Rev. Lett. 78, 3535–3538 (1997)
Holst, T., Esteve, D., Urbina, C. & Devoret, M. H. Effect of a transmission line resonator on a small capacitance tunnel junction. Phys. Rev. Lett. 73, 3455–3458 (1994)
Hofheinz, M. et al. Bright side of the Coulomb blockade. Phys. Rev. Lett. 106, 217005 (2011)
Romero, G., Lizuain, I., Shumeiko, V. S., Solano, E. & Bergeret, F. S. Circuit quantum electrodynamics with a superconducting quantum point contact. Phys. Rev. B 85, 180506 (2012)
Sköldberg, J., Löfwander, T., Shumeiko, V. S. & Fogelström, M. Spectrum of Andreev bound states in a molecule embedded inside a microwave-excited superconducting junction. Phys. Rev. Lett. 101, 087002 (2008)
Mourik, V. et al. Signatures of Majorana fermions in hybrid superconductor-semiconductor nanowire devices. Science 336, 1003–1007 (2012)
We acknowledge technical assistance from P. Sénat and P.-F. Orfila, theoretical input from M. Houzet, help in the experiments from L. Tosi, and discussions with V. Shumeiko, A. Levy-Yeyati and within the Quantronics group. This work was supported by ANR contracts DOCFLUC and MASH, and by C’Nano. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement no. PIIF-GA-2011-298415.
The authors declare no competing financial interests.
About this article
Cite this article
Bretheau, L., Girit, Ç., Pothier, H. et al. Exciting Andreev pairs in a superconducting atomic contact. Nature 499, 312–315 (2013). https://doi.org/10.1038/nature12315
npj Quantum Information (2021)
Nature Reviews Materials (2021)
Nature Reviews Physics (2020)
Nature Physics (2020)
Nature Physics (2020)