In practical quantum computing implementations, qubits are stored using physical systems that can exhibit quantum properties and be controlled and manipulated to perform quantum computations. There are several physical platforms that can be used to realize qubits, each with its own advantages and challenges. I'll mention a few common approaches:
Superconducting qubits: These are based on circuits made of superconducting materials. Superconducting qubits use the quantum behavior of superconducting circuits, such as Josephson junctions, to encode and manipulate quantum information.
Trapped ion qubits: These qubits are realized using individual ions trapped and controlled using electromagnetic fields. The internal energy levels of the trapped ions serve as the basis states for encoding qubit information.
Quantum dot qubits: Quantum dots are tiny semiconductor structures that can trap and manipulate individual electrons. The quantum state of the electron's spin can be used to encode and store qubit information.
Topological qubits: These qubits are based on exotic states of matter called topological states. Topological qubits rely on the stability of non-local properties to store and manipulate quantum information.
Regardless of the physical platform, the key aspect is that these systems provide a means to encode and manipulate quantum information. The qubit's quantum state, such as a superposition of |0⟩ and |1⟩, is realized through the manipulation of the physical properties of the underlying system.
It's important to note that maintaining the coherence and stability of qubits is a significant challenge in quantum computing. Quantum information is fragile and can easily be disrupted by environmental noise and interactions with the surrounding environment. Techniques such as error correction and error mitigation are employed to enhance the stability and reliability of qubit storage and operations.
Overall, storing qubits involves utilizing physical systems that can exhibit quantum properties and be controlled to encode, manipulate, and maintain the quantum information throughout the computation process.