Viewers of quantum events are also subject to uncertainty

It gets better. What if B is also bound to a quantum object in a superposition of two sites? Hence the quantum state of A is now entangled in two different ways, depending on the possible locations of B. Since determining the quantum state of B determines the state of A, A and B are now entangled.

Renato Renner, a physicist at the Swiss Federal Institute of Technology in Zurich, believes that careful study of quantum reference frames will resolve paradoxes in our understanding of the quantum world.

Credit: Julia Marthaler

In the example above, two fundamental properties of quantum systems – superposition and entanglement – ​​are shown to depend on the reference frame. “The main message is that a lot of the properties that we think are so important, absolutely, are relational,” he said. Anne Catherine de la Hametteco-author of the recent paper.

Even the order of events succumbs to the harshness of quantum reference frames. For example, from a single frame of reference, we may observe a detector click occurring at a particular time. But with a different frame of reference, the click might end up in a superposition that occurs before and after another event. Whether you notice the click occurring at a particular time or whether it is a superposition of different orders of events depends on the choice of frame of reference.

Step into gravity

Researchers hope to use these shifting quantum perspectives to understand the puzzling nature of gravity. Einstein’s general relativity, a classic theory of gravity, says that gravity is the distortion of the fabric of space-time by a massive object. But how would spacetime warp if the same object were in a superposition of two locations? “This question is very difficult to answer using usual quantum physics and gravity,” he said. Victoria Capela researcher in Bruckner’s group and a co-author of the new paper.

Switch to a frame of reference whose origin is in a superposition state, and the massive object can end up at a specific location. It is now possible to calculate the gravitational field. “By finding a suitable quantum frame of reference, we can take a problem we can’t solve (and make it) a problem we can only use known standard physics to solve,” Capel said.

Such changes in perspective should be useful for analysis Future experiments Which aims to place very small blocks in overlays. For example, physicists Chiara Marlitto and Vlatko Federal From the University of Oxford they have Suggested Place two masses in a superposition of two positions and then study how this affects their gravitational fields. Emerging attempts to formally describe quantum frames of reference can help understand these investigations into the interaction between gravity and quantum theory, a fundamental starting point for the theory of quantum gravity.