A large-scale object, like a dust grain or massive sphere, exhibiting quantum behavior.A macroscopic quantum object is a physical system large enough to be visible or tangible, yet it exhibits quantum mechanical properties such as superposition or entanglement. This challenges the classical intuition that large objects always behave deterministically. Examples include superconducting circuits, optomechanical resonators, and levitated nanoparticles. Studying these objects tests the boundary between quantum and classical worlds and could enable new technologies like quantum sensors and quantum computers.
The idea dates back to Schrödinger's 1935 thought experiment, but experimental realization began in the 21st century with mechanical resonators. Notable milestones include cooling a macroscopic mirror to its quantum ground state in 2009 and entangling two macroscopic objects in 2021.
To make a macroscopic object quantum, it must be isolated from its environment to prevent decoherence—the loss of quantum coherence due to interactions with heat, vibration, or light. Techniques include cooling to near absolute zero, suspending the object in a vacuum, and using laser cooling to reduce its motion to the quantum ground state. Once isolated, the object's center-of-mass motion can be placed in a superposition of two locations, or its vibrational modes can be entangled with photons.
Used in quantum sensing for measuring tiny forces, accelerations, and gravitational fields, and as testbeds for quantum mechanics in new regimes.
In 2021, researchers entangled two vibrating drumheads each about the width of a human hair, demonstrating quantum entanglement in objects visible to the naked eye.
| I | variable | Moment of inertia — moment of inertia kilogram metre squared |
| k | variable | Dimensionless shape factor |
| M | variable | Mass of the sphere — mass kilogram |
| R | variable | Radius of the sphere — radius metre |
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