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Quantum technology researchers at Chalmers University of Technology have successfully developed a technique to control the quantum state of light in a three-dimensional cavity. In addition to generating the already known states, the researchers demonstrate for the first time the long-sought cubic phase state. This breakthrough is an important step towards efficient error correction in quantum computers.
Simone Gasparinetti, leader of the Experimental Quantum Physics Research Group at Chalmers University and one of the first authors of the study, said:
Just as classical computers are based on bits that can take the values 0 or 1, the most common way to build quantum computers uses a similar approach. Quantum mechanical systems with two different quantum states, so-called quantum bits (qubits), serve as building blocks.
One of the quantum states is assigned the value 0 and the other quantum state is assigned the value 1. However, the quantum mechanical state of superposition allows a qubit to occupy both states 0 and 1 at the same time. This allows quantum computers to process massive amounts of data and solve problems well beyond the reach of today’s supercomputers.
These states can be compared to a guitar string vibrating in different ways. This method is called continuously variable quantum computing and allows to encode the values 1 and 0 in several quantum mechanical states of the resonator.
A major obstacle to achieving practical quantum computers is that the quantum systems used to encode information are susceptible to noise and interference, leading to errors. Correcting these errors is a key challenge in the development of quantum computers. A promising approach is to replace qubits with resonators (quantum systems with many defined states instead of two).
However, controlling the state of the cavity is a challenge that quantum researchers around the world are grappling with. Chalmers’ results provide an opportunity to do so. The technique developed at Chalmers allows researchers to explore previously documented quanta of light, such as the Schrödinger cat or Gottesmann-Kitayev-Preskil (GKP) state, as well as the cubic phase state, which has only been described theoretically. Almost any state can be generated.
“The cubic phase state is something many quantum researchers have been trying to create in practice for 20 years. To be able to do this for the first time is a testament to how well our technology works. But that’s the most important thing, you can,” says Marina Kudla, a PhD student at the Institute for Microtechnology and Nanosciences and lead author of the study.