Researchers at Chalmers University of Technology have successfully developed a technique to control quantum states of light in a three-dimensional cavity. This development will pave the way for solving errors in quantum technology.
In addition to creating previously known states of light, the team are the first to demonstrate the long-sought cubic phase state.
Similar to conventional computers, which are based on bits that can take the value of zero or one, quantum technology computers are built using two different quantum states known as quantum bits. One quantum bit is assigned the value of zero and the other one.
Qubits can assume both states of zero and one simultaneously. This allows a quantum computer to process huge amounts of data, with the possibility of solving problems far beyond the reach of today’s technology.
Common errors with quantum computers
A major obstacle towards the integration of quantum technology into everyday life is that the systems used to encode their information are prone to noise and interference, causing errors.
Correcting these errors has become a huge challenge in the technology industry. Researchers have proposed the best method is to replace qubits with resonators, where the quantum technology would have a large number of defined states rather than two.
However, controlling the state of a resonator has proved to be a challenge in itself. The team at Chalmers have proved there is a way to do this, as the technique allows researchers to generate all previously demonstrated quantum states of light, including the cubic phase state.
“The cubic phase state is something that many quantum researchers have been trying to create in practice for twenty years. The fact that we have now managed to do this for the first time is a demonstration of how well our technique works, but the most important advance is that there are so many states of varying complexity, and we have found a technique that can create any of them,” explained Marina Kudra, a doctoral student at the Department of Microtechnology and Nanoscience, and the study’s lead author.
The future of quantum technology: controlling the state of resonators
The resonator constructed by the team is a three-dimensional superconducting cavity, and is made of aluminium. Complex superpositions of photons trapped inside it are generated by interaction with a second superconducting circuit.
The quantum mechanical properties of the photons are controlled by applying a set of electromagnetic pulses, known as gates. The researchers used an algorithm to optimise a specific sequence of simple displacement gates and complex SNAP-gates, which generate the state of photons.
The team faced challenges throughout the process, one being that the complex gates were too long. To overcome this, they made the SNAP-gates shorter by using advanced control methods to optimise the electromagnetic pulses.
“The drastic improvement in the speed of our SNAP gates allowed us to mitigate the effects of decoherence in our quantum controller, pushing this technology one step forward. We have shown that we have full control over our quantum mechanical system,” said Simone Gasparinetti, head of experimental quantum physics at Chalmers.
The team argued that their new development in quantum technology is “on par with the best in the world.” Their main goal is to develop a fully-scalable, integrated quantum computer that is free from qubit errors.
