Researchers at Chalmers University of Technology have developed a method for controlling the quantum states of light in a three-dimensional cavity. The researchers are the first to demonstrate the long-sought cubic phase state, in addition to producing previously known states. The breakthrough is a significant step toward error correction efficiency in quantum computers.
Simone Gasparinetti, head of the experimental quantum physics research group at Chalmers and one of the study’s senior authors, states, “We have demonstrated that our technology is on par with the best in the world.”
In the same way that a conventional computer is based on bits that can take the value 0 or 1, the most prevalent method for constructing a quantum computer employs the same approach. As building blocks, quantum mechanical systems with two distinct quantum states, known as quantum bits (qubits), are utilized. The value 0 is assigned to one of the quantum states, and the value 1 to the other. But because of the state of superposition in quantum mechanics, qubits can be in both the 0 and 1 states at the same time. This means that a quantum computer could process huge amounts of data and possibly solve problems that today’s supercomputers can’t.
First time ever for cubic phase state
The quantum systems used to encode information are susceptible to noise and interference, which leads to inaccuracies, which is a significant barrier to the development of a practical quantum computer. This is a significant obstacle in the development of quantum computers. A promising strategy is to replace qubits with resonators—quantum systems with a large number of distinct states rather than just two. These conditions are comparable to those of a guitar string, which can vibrate in a variety of ways. The method is known as continuous-variable quantum computing, and it enables the encoding of 1 and 0 in multiple quantum mechanical states of a resonator. However, controlling the states of a resonator, however, is a challenge with which quantum researchers from around the world are struggling. And Chalmers’ findings provide a means to do so. The technique developed at Chalmers enables researchers to generate virtually all previously demonstrated quantum states of light, such as Schrodinger’s cat or Gottesman-Kitaev-Preskill (GKP)states, as well as the cubic phase state, a state previously only described in theory.
“Numerous quantum researchers have spent twenty years attempting to create in practice the cubic phase state. The fact that we have now accomplished this feat for the first time demonstrates the efficacy of our technique, but the most significant advancement is that we have discovered a technique that can generate any state of varying complexity. ” The study’s lead author, a doctoral student in the Department of Microtechnology and Nanoscience, is Marina Kudra.
Improvement in gate speed
The resonator is an aluminum superconducting cavity in three dimensions. Complex superpositions of photons are made when the resonator interacts with a secondary superconducting circuit.
Controlling the quantum mechanical properties of photons by applying electromagnetic pulses called gates The researchers were able to optimize a specific sequence of simple displacement gates and complex SNAP-gates to generate the photons’ state using an algorithm. When it was determined that the complex gates were too long, the researchers found a way to shorten them by optimizing the electromagnetic pulses with optimal control methods.
“The significant increase in speed of our SNAP gates enabled us to mitigate the effects of decoherence in our quantum controller, advancing this technology. We have demonstrated complete command over our quantum mechanical system, “says Simone Gasparinetti.
Or, to use a more poetic expression:
Marina Kudra states, “I captured light in a place where it thrives and shaped it into some truly beautiful forms.”
Obtaining this result also depended on the superiority of the physical system (the aluminium resonator itself and the superconducting circuit.) Marina Kudra has demonstrated in the past how the aluminium cavity is created by first milling it and then making it incredibly clean using techniques such as heating it to 500 degrees Celsius and washing it with acid and solvent. Together with the Swedish company Intermodulation Products, the electronics that apply the electromagnetic gates to the cavity were made.
Research as part of the WACQT programme
The research was conducted at Chalmers under the auspices of the Wallenberg Centre for Quantum Technology (WACQT), a comprehensive research program designed to position Swedish research and industry at the forefront of quantum technology. The main goal of the project, which is being led by Professor Per Delsing, is to make a quantum computer.
At Chalmers, we have everything necessary to construct a quantum computer, from theory to experimentation, all under one roof. “Error correction is a significant bottleneck in the development of large-scale quantum computers, and our results are evidence of our culture and working methods,” says Per Delsing.
