Pilot Project on Quantum Computing

In this collaborative project with IBM we will develop model Hamiltonians (generalised spin boson systems) for quantum computing, with focus on the effects of different models for the environment on the qbits. The different models will be tested comparing MCTDH, linearised and other mixed quantum-classical schemes.

Improving Quantum Logical Gates

A universal quantum logical gate is one of the key components of the universal quantum computer. It enables any quantum computational algorithm to be easily programmed into the real quantum computer by avoiding the hard-coded pre-determined logical gates that limit the number of different gate types a quantum algorithm can use. For this reason, designing an effective universal quantum gate is one of the major goals in the development of quantum computers. Here we are specifically interested in the design and further optimisation of the universal quantum gates between qubits made of superconducting transmon coupled via a tunable qubit.

The Local Control Theory (LCT) was used for the construction of the control pulses. For a brief description of the LCT click here. Construction of two pulse types using LCT was examined so far. Pulses were constructed for systems made of two or more fixed frequency transmon qubits all coupled to a single tunable qubit, whose frequency is precisely tuned by the control pulse:

Schematic representation of a two fixed frequency qubits (blue and orange) system coupled to a tunable qubit (green) whose frequency is controlled by the magnetic flux (red arrows) through its SQUID loop element (black dashed circle) generated by the electric current in the high-speed flux line (dark blue). [Figure adapted from here.]

One of the simplest generated pulses is the state preparation pulse displayed in Figure 1 for a complete population transfer from one qubit state (blue) to another qubit state (orange). This pulse was obtained directly from LCT without any optimization. Applying an additional optimization procedure it can be further shortened and made to drive the population also in the reverse direction. More information will be available soon in an upcoming per-review paper.