There are several factors that currently limit the increase in the number of qubits in quantum computers. Some of the main challenges include:
Quantum decoherence: Quantum systems are extremely delicate and prone to errors caused by interactions with the environment. These errors accumulate as the number of qubits increases, making it difficult to maintain the coherence and reliability of the quantum information. Extending the coherence time and reducing errors require significant advancements in error correction techniques and error mitigation strategies.
Technical constraints: Building and controlling qubits is a complex engineering task. Currently, most quantum computers use superconducting qubits or trapped ion qubits, which have their own technical limitations. Increasing the number of qubits requires addressing challenges such as scaling up fabrication processes, improving the quality of qubits, and developing efficient methods for qubit control and interconnection.
Physical resources: Quantum computers require a highly controlled environment with extremely low temperatures and low levels of noise. Cooling systems, shielding, and other infrastructure are necessary to maintain the stability required for qubit operation. As the number of qubits increases, the physical resources required also grow, posing challenges in terms of scalability and cost.
Quantum error correction: Quantum error correction is a vital aspect of building large-scale, fault-tolerant quantum computers. However, implementing error correction codes and protocols is a complex task that introduces additional overhead in terms of the number of physical qubits required for error correction. The overhead can be significant, making it challenging to scale up quantum computers while maintaining a reasonable number of qubits for computational tasks.
Control and connectivity: Controlling and interconnecting qubits become increasingly challenging as their number grows. Ensuring high-fidelity and precise control over individual qubits, as well as enabling efficient communication and entanglement between qubits, is crucial for quantum computation. Developing robust control systems and scalable interconnection schemes is an ongoing area of research.
While these challenges exist, researchers and engineers are actively working to overcome them. Continued progress in quantum technologies, novel qubit designs, error correction techniques, and improved control methods will likely contribute to the future increase in the number of qubits and the development of more powerful quantum computers.