Quantum coherence refers to a fundamental property of quantum systems, wherein the quantum states of particles or systems can exist in a superposition of multiple states simultaneously. It is a key aspect of quantum mechanics that distinguishes it from classical physics.
In classical physics, systems have well-defined states that can be precisely determined and described. However, in the quantum realm, particles can exist in states that are a combination or superposition of multiple possibilities. This superposition arises due to the wave-like nature of particles at the quantum level.
Quantum coherence allows particles to exist in a state that is a linear combination of multiple basis states. For example, a qubit, the basic unit of quantum information, can exist in a superposition of both 0 and 1 states. This means that before measurement, the qubit can be in a state that represents both 0 and 1 at the same time, with specific probabilities assigned to each outcome.
The superposition and coherence of quantum states enable certain computational advantages in quantum computing algorithms and can also be harnessed for secure communication protocols, such as quantum cryptography.
However, maintaining quantum coherence is challenging due to the susceptibility of quantum systems to environmental disturbances and decoherence. Interactions with the surrounding environment, such as temperature changes or interactions with other particles, can cause the superposition to collapse, leading to the loss of coherence and the system collapsing into a well-defined state.
Efforts are made to mitigate decoherence and maintain coherence in quantum systems, such as through error correction techniques, quantum error correction codes, and various methods to isolate quantum systems from their environments.
In summary, quantum coherence refers to the property of quantum systems that allows them to exist in superpositions of multiple states simultaneously, offering unique computational and informational advantages.