Superconducting quantum computers use superconducting electrical circuits as qubits in a quantum processor. These circuits operate at extremely low temperatures, where electrical current can flow with negligible resistance.
The qubit’s logical states, |0⟩ and |1⟩, correspond to two energy levels of the circuit. A general qubit state can therefore be written as
|ψ⟩ = α|0⟩ + β|1⟩
where the coefficients determine the measurement probabilities. [1.7]
A superconducting quantum computer is a quantum computer that uses superconducting electronic circuits as qubits in a quantum processor.
Qubit encoding
The qubit state is encoded in properties of Josephson junctions, which are nonlinear superconducting elements.
Different qubit types exploit these properties in various ways:
Charge qubits: Encode information in the number of Cooper pairs.
Flux qubits: Encode information in magnetic flux states.
Transmon qubits: A modified charge qubit design that reduces sensitivity to noise.
Advantages
Scalability: Circuits can be fabricated using semiconductor manufacturing techniques.
Fast operations: Gate times are on the order of nanoseconds.
Integration: Compatible with microwave control systems and cryogenic electronics.
Challenges
Decoherence: Qubits lose quantum information due to environmental noise.
Error correction: Requires many physical qubits to form reliable logical qubits.
Cryogenics: Must be cooled to millikelvin temperatures using dilution refrigerators.
Applications
Used by major platforms like IBM Quantum, Google Quantum AI, and Rigetti Computing.
Suitable for running algorithms such as Shor’s Algorithm and Quantum Phase Estimation once fault tolerance is achieved.
