Decoherence is indeed one of the major challenges faced by quantum computers. It refers to the loss of quantum coherence, where a quantum system interacting with its environment causes the quantum states to become entangled with the surrounding environment, leading to a loss of the delicate quantum properties that quantum computers rely on for computation.
While complete elimination of decoherence is currently not possible, quantum computers employ several techniques to mitigate its effects and minimize errors:
Quantum Error Correction (QEC): Quantum error correction is a method that utilizes redundancy and entanglement to protect quantum information from errors caused by decoherence. QEC algorithms encode logical qubits (the basic units of quantum information) into a larger number of physical qubits, allowing errors to be detected and corrected through error-correcting codes. By distributing and redundantly storing quantum information across multiple physical qubits, QEC can help preserve coherence and protect against decoherence-induced errors.
Quantum Error Avoidance: Quantum error avoidance techniques aim to design quantum algorithms in such a way that they are less sensitive to errors caused by decoherence. This can involve restructuring algorithms to minimize the impact of errors or designing error-tolerant protocols that can still achieve accurate results even in the presence of errors.
Decoherence Time and Quantum Gates: Quantum computer hardware strives to increase the coherence time, which is the duration during which qubits can retain their quantum properties before decoherence occurs. Longer coherence times allow for more reliable computations. Additionally, quantum gates (operations performed on qubits) are optimized to be as fast as possible to reduce the time during which errors can occur.
Environmental Control and Cryogenics: Quantum computers are typically operated in carefully controlled environments to minimize interactions with the surrounding environment. Extremely low temperatures are often employed, as it slows down the effects of decoherence. Cryogenic systems are used to cool quantum processors to temperatures close to absolute zero, reducing environmental interference.
It's worth noting that despite these techniques, decoherence remains a significant challenge, and quantum error rates are still relatively high. Ongoing research and engineering efforts are focused on improving error mitigation strategies, developing better qubits, and refining the overall design of quantum systems to enhance their resistance to decoherence and improve the reliability of quantum computations.