New technique to control quantum states of light in a three-dimensional cavity

Quantum technology reaches unprecedented control over captured light.


The fact that the information is encoded using quantum systems that are susceptible to noise and interference, which results in errors, is a significant barrier to the development of a realistically viable quantum computer. The development of quantum computers faces a major difficulty in correcting these errors. Replacing qubits with resonators, quantum systems with more specified states than simply two, offers a viable alternative. These states may be compared to a guitar string, which can vibrate in many different ways.

However, controlling the states of a resonator is a challenge. Now, quantum technology at the Chalmers University of Technology has developed a technique to control the quantum states of light in a three-dimensional cavity. The technique allows scientists to generate virtually all previously demonstrated quantum states of light.

Simone Gasparinetti, who is head of a research group in experimental quantum physics at Chalmers and one of the study’s senior authors, said, “We have shown that our technology is on par with the best in the world.”

Marina Kudra, a doctoral student at the Department of Microtechnology and Nanoscience and the study’s lead author, said, “The cubic phase state is something that many quantum scientists have been trying to create in practice for twenty years. The fact that we have now managed to do this for the first time demonstrates 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.” 

Scientists controlled the quantum mechanical properties of photons by applying a set of electromagnetic pulses called gates. They used an algorithm to optimize a specific sequence of simple displacement gates and complex SNAP gates to generate the state of the photons. When the complex gates turned out to be excessively long, the scientists discovered a solution to shorten them by maximizing the electromagnetic pulses with optimum control techniques.

Simone Gasparinetti said, “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 full control over our quantum mechanical system.”

Marina Kudra said, “Or, to put it more poetically, I captured light in a place where it thrives and shaped it in some truly beautiful forms.”

A superior physical system was also necessary to achieve this objective.

Per Delsing said“At Chalmers, we have the full stack for building a quantum computer, from theory to experiment, all under one roof. Solving the challenge of error correction is a major bottleneck in developing large-scale quantum computers, and our results are proof of our culture and ways of working.”

Journal Reference:

  1. Marina Kudra, Mikael Kervinen, Ingrid Strandberg, et al. Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences. PRX Quantum. DOI: 10.1103/PRXQuantum.3.030301


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