Quantum memory

Quantum memory is a device that stores quantum states — typically the polarization, spin, or energy level of a particle — for a period long enough to be useful in quantum information processing. Unlike classical memory, which stores bits as stable voltage levels, quantum memory must preserve the coherence and superposition of quantum states without measuring them, which would destroy the information.

The primary use of quantum memory is in quantum repeaters, where it stores entangled states while classical communication coordinates Entanglement swapping. It is also essential for synchronizing operations in distributed quantum computing and for buffering quantum states in a Quantum internet.

The challenge is decoherence: interaction with the environment destroys quantum states over time. Current quantum memory technologies — trapped ions, rare-earth doped crystals, atomic ensembles — achieve storage times ranging from microseconds to hours, with varying fidelity. The race to build quantum memory that is long-lived, high-fidelity, and scalable is one of the defining engineering problems of the field.