Edging towards the quantum speed limit

More rapid energy progression in a quantum computer may be achieved thanks to more rapid jumps in energy in a quantum state.

Quantum researchers at Aalto University sped up the energy progression in a transmon chip – a custom-designed electrical circuit used in quantum computing – by making it adsorb two different microwave photons at the same time.

Energy levels of the transmon jumped more than one level in one go, potentially allowing for more rapid energy progression in quantum devices.

Dr. Sergey Danilin at Aalto University said: 'To get a useful quantum system, you need to imagine climbing a ladder while holding a glass of water, it works if one does it smoothly – but if you do it too fast the water will be spilled. Certainly this requires a special skill.”

The energy of the transmon can take only specific values, called energy levels. When microwaves are shined on the circuit, the transmon can climb up an energy level.

By continuously correcting the state of the system, at temperatures a few thousandths of a degree above absolute zero, the scientists were able to drive this process more rapidly and at high fidelity.

The laws of nature restrict how fast a quantum energy switch can take place –known as the quantum speed limit. But Aalto found that their new method resulted in changes in energy level that took place at speeds close to theoretically calculated limit.

The research could have significance in quantum computing and quantum simulation applications that require fast operations such as state preparation and the creation of quantum gates.

Docent Sorin Paraoanu, leader of the research group, said: We would like to understand more deeply the processes related to energy transfer, which are ubiquitous in the natural world and in the technological marvels that surround us. For example, are there any fundamental limits to how fast we can charge the battery of an electric car?”

The team published its work in Science Advances.