Unlike typical conductors, superconductors possess a [[critical temperature]] at which resistivity plummets to zero and conductivity is drastically increased. In superconductors, the basic charge carriers are pairs of [[electron]]s (known as [[Cooper pairs]]), rather than single [[fermion]]s as found in typical conductors.<ref>{{Cite web |title=Cooper Pairs |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/coop.html }}</ref> Cooper pairs are loosely bound and have an energy state lower than that of [[Fermi energy|Fermi Energy]]. Electrons forming Cooper pairs possess equal and opposite momentum and spin so that the total [[Spin (physics)|spin]] of the Cooper pair is an [[integer]] spin. Hence, Cooper pairs are [[boson]]s. Two such superconductors which have been used in superconducting qubit models are [[niobium]] and [[tantalum]], both d-band superconductors.<ref>{{Cite journal |last=Shen |first=L. Y. L. |date=1972-02-01 |title=Superconductivity of Tantalum, Niobium and Lanthanum Studied by Electron Tunneling: Problems of Surface Contamination |url=https://aip.scitation.org/doi/abs/10.1063/1.2946195 |journal=AIP Conference Proceedings |volume=4 |issue=1 |pages=31–44 |doi=10.1063/1.2946195 |bibcode=1972AIPC....4...31S |issn=0094-243X|url-access=subscription }}</ref>
==== Bose–Einstein condensates ====
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=== Unimon ===
In 2022 researchers from [[IQM (Quantum Computers)|IQM]] Quantum Computers, [[Aalto University]], and [[VTT Technical Research Centre of Finland|VTT Technical Research Centre]] of Finland discovered a novel superconducting qubit known as the Unimon.<ref>{{Cite web |title=Unimon: A new qubit to boost quantum computers from IQM |url=https://www.meetiqm.com/articles/press-releases/iqm-unimon-qubit/ |access-date=2022-12-12 |website=www.meetiqm.com |language=en}}</ref> A relatively simple qubit, the Unimon consists of a single Josephson junction shunted by a linear inductor (possessing an inductance not depending on current) inside a (superconducting) [[resonator]].<ref name="Buchanan-2022">{{Cite journal |last=Buchanan |first=Mark |date=2022-12-08 |title=Meet the Unimon, the New Qubit on the Block |url=https://physics.aps.org/articles/v15/191 |journal=Physics |language=en |volume=15|page=191 |doi=10.1103/Physics.15.191 |bibcode=2022PhyOJ..15..191B |s2cid=257514449 |doi-access=free }}</ref> Unimons have increased anharmonicity and display faster operation time resulting in lower susceptibility to noise errors.<ref name="Buchanan-2022" /> In addition to increased anharmonicity, other advantages Unimon qubit include decreased susceptibility to flux noise and complete insensitivity to dc charge noise.<ref name="Hyyppä-2022" />
