Putting macroscopic objects into quantum entanglement will open up whole new applications.
Quantum entanglement is one of the most perplexing, and perhaps eventually useful, areas of quantum physics. So far, it has been relegated mostly to the microscopic world of particles. But scientists at the Niels Bohr Institute at the University of Copenhagen recently have put two very different macroscopic objects in entanglement - opening up entirely new applications for quantum entanglement.
What is Quantum Entanglement?
Quantum Entanglement is a tricky concept to understand - and that’s because it is so counterintuitive. Imagine two particles on opposite ends of the Universe. These particles can have properties that are unknown until they are measured. For example, let’s say that these particles can be measured as red or blue. When one particle is measured to be red, its entangled pair will also be red. But the strange thing is - this is not an inherent property of the particles. Instead, the measured particle decides to be red once it is measured, and somehow communicates that choice across the Universe to its entangled friend - seemingly faster than the speed of light. This is shown by the Bell Theorem, and has been scientifically supported in a number of ways.
When one particle of an entangled pair is measured as red, the other will also be red, no matter ... [+]
Moving Entanglement to the Macroscopic World
Until recently, the concept of entanglement has been confined to the very small microscopic world. But in recent years, this has moved to larger and larger objects. (A group in 2018 succeeded in putting objects 20 microns across in an entangled state).
This time, a group from the Niels Bohr Institute at the University of Copenhagen succeeded in putting two very different objects into entanglement with one another - the motion of a mechanical oscillator, or a drum, several millimeters long and 13nm thick, and a cloud of a billion cesium atoms acting as a collective atomic spin oscillator. As photons passed between the two objects, they became entangled, so that the motion of the drum became correlated with the cloud of atoms.
Putting different macroscopic materials in an entangled state is a big deal. “The bigger the objects, the further apart they are, the more disparate they are, the more interesting entanglement becomes from both fundamental and applied perspectives,” says one of the authors, Professor Eugene Polzik. “With the new result, entanglement between very different objects has become possible”.
Applications of Entanglement
Quantum entanglement has applications from cryptography to quantum computing. One particularly interesting application relates to LIGO - the Laser Interferometer Gravitational Observatory.
LIGO looks for gravitational waves - ripples in spacetime caused by events such as merging black holes, stars exploding, or the Big Bang. When events like this happen, they stretch and compress spacetime itself, sort of like ripples traveling outwards across a pond.
LIGO can detect the merger of two orbiting black holes through the ripples they create in spacetime ... [+]
LIGO is made of laser interferometers within huge arms at right angles to one another, each 4 km long. At the end of each arm is a mirror. A beam of light is sent down each arm, bouncing off the mirror and returning to its starting point, where it interacts with itself. The light waves either combine with one another (constructive interference) or cancel each other out (destructive interference). Doing this, LIGO can measure very small changes in distance.
If a gravitational wave passes through LIGO, one arm is slightly stretched, while another is slightly compressed. This effect is very small, but can be measured.
Unfortunately, LIGO is fundamentally limited by zero-point energy. Even at zero Kelvin, particles will wobble, which causes a fuzziness in LIGO’s measurements that can limit its sensitivity.
But quantum entanglement could come to the rescue. If LIGO’s mirrors could be put in quantum entanglement with an atomic cloud, this uncertainty in zero-point energy can be removed.
