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# '''A scalable physical system with well characterized qubits.''' "Well characterized implies that that [[Hamiltonian mechanics|Hamiltonian function]] must be well-defined i.e the energy eigenstates of the qubit should be able to be quantified.. A scalable system is self-explanatory, it indicates that this ability to regulate a qubit should be augmentable for multiple more qubits. Herein lies the major issue Quantum Computers face, as more qubits are implemented it leads to a exponential increase in cost and other physical implementations which pale in comparison to the enhanced speed it may offer.<ref name="qc-at-davis.github.io"/> As superconducting qubits are fabricated on a chip, the many-qubit system is readily scalable. Qubits are allocated on the 2D surface of the chip. The demand for well characterized qubits is fulfilled with (a) qubit non-linearity (accessing only two of the available energy levels) and (b) accessing a single qubit at a time (rather than the entire many-qubit system) by way of per-qubit dedicated control lines and/or frequency separation, or tuning out, of different qubits.
# '''Ability to initialize the state of qubits to a simple fiducial state.'''<ref name="DiVincenzo-2008">{{Cite journal |last=DiVincenzo |first=David |date=February 1, 2008 |title=The Physical Implementation of Quantum Computation |journal=IBM T.J. Watson Research Center|volume=48 |issue=9–11 |pages=771–783 |doi=10.1002/1521-3978(200009)48:9/11<771::AID-PROP771>3.0.CO;2-E |arxiv=quant-ph/0002077 |bibcode=2000ForPh..48..771D |s2cid=15439711 }}</ref> A fiducial state is one that is easily and consistently replicable and is useful in quantum computing as it may be used to guarantee the initial state of qubits. One simple way to initialize a superconducting qubit is to wait long enough for the qubits to relax to the ground state. Controlling qubit potential with tuning knobs allows faster initialization mechanisms.
# '''Long relevant decoherence times'''<ref name="DiVincenzo-2008" />'''.''' Decoherence of superconducting qubits is affected by multiple factors. Most decoherence is attributed to the quality of the Josephson junction and imperfections in the chip substrate. Due to their mesoscopic scale, superconducting qubits are relatively short lived. Nevertheless, thousands of gate operations have been demonstrated in these many-qubit systems
# '''A “universal” set of quantum gates.'''<ref name="DiVincenzo-2008" /> Superconducting qubits allow arbitrary rotations in the Bloch sphere with pulsed microwave signals, implementing single qubit gates. <math>\sigma_z \sigma_z</math> and <math>\sigma_x \sigma_x</math> couplings are shown for most implementations and for complementing the universal gate set
|journal=Nature Physics |date=16 January 2024 |volume=20 |issue=1 |pages=240-246 |doi=10.1038/s41567-023-02326-7 |bibcode=2024NatPh..20..240N |doi-access=free |arxiv=2211.10383}}</ref>. This criterion may also be satisfied by coupling two transmons with a coupling capacitor.<ref name="docs.pennylane.ai" />
# '''Qubit-specific measurement ability.'''<ref name="DiVincenzo-2008" /> In general, single superconducting qubits are used for control or for measurement.
# '''Interconvertibility of stationary and flying qubits.'''<ref name="DiVincenzo-2008" /> While stationary qubits are used to store information or perform calculations, flying qubits transmit information macroscopically. Qubits should be capable of converting from being a stationary qubit to being a flying qubit and vice versa.
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