To preserve encrypted quantum data for more than 5 seconds, they had to cool the molecular gas to almost absolute zero.
British scientists have created ultra-cold storage that preserves the stability of the qubits that underlie quantum computers. They published an article about their achievement in the journal Nature Physics.
One of the main problems preventing the creation of a reliable quantum computer is decoherence, a physical process that causes fluctuations in the environment to destroy the information recorded in the particles. Employees at the Joint Quantum Center at Durham University have found a way to significantly increase the performance of qubits in ultracold polar molecules, which are used as memory storage.
They took gaseous molecules of cesium and rubidium atoms, which were cooled to almost absolute zero temperature (-273.15 degrees Celsius). As the authors of the article explained, such chemical elements are well suited for the creation of qubits due to their complex structure with internal vibrations and rotations. As a result, the data in the quantum system managed to keep longer than 5.6 seconds – a time many times longer than was achieved in other systems of this type. At the same time, the qubits “lived” longer than the gas they were in.
During the study, the team measured the coherence of the quantum system (coherence), then encrypted the information in the qubits with microwaves and watched how they behaved. They measured coherence at equal intervals and found that the number of molecules in any state changes perodically, and the amplitude of oscillations decreases when information is lost.
As it turned out, the stability time can be affected by a magnetic field or a polarizing laser that creates optical traps for the molecules. The scientists selected such field parameters that the qubits did not respond to small variations in intensity. The maximum duration was given by laser radiation directed into the magnetic field at an angle of about 55 degrees. Now British scientists are trying to improve optical traps for cooled molecules to use in quantum computers.