Research

Our work is on quantum computation, both theoretical and experimental.

Quantum Algorithms

New small size quantum computers are coming to age. A relevant example is the IBM Quantum Experience which is accessible on the cloud. The use of such a machine brings the possibility of exploring new quantum algorithms.

There are two main lines of research in quantum algorithmia. A first possibility is to use pure quantum logic based on gates that build circuits. The fact that the readout of a quantum machine is non-deterministic brings an element of difficulty to the construction of quantum algorithms and its application to real problems. A second possibility consists in dropping the quantum circuit philosophy in favor of a quantum annealing strategy. This second solution makes feasible attacking optimization problems, which are relevant for different industries.

The focus of Quantic on quantum algorithms can be summarized as follows:

1) Develop strategies to exploit small and medium size quantum computers
2) Adapt realistic problems to quantum annealing
3) Develop a quantum operating system to run a small quantum device

Example of a quantum circuit that generalizes GHz-like states and measures them in order to verify Mermin inequalities. From “Experimental test of Mermin inequalities on a 5-qubit quantum computer”, D. Alsina, J. I. Latorre, Phys. Rev. A 94, 012314 (2016), arxiv:1605.04220v2
Superconducting quantum processors

We build quantum processors out of superconducting quantum circuits. Superconducting qubits are constructed using Josephson junctions, which are nonlinear, nondissipative elements that generate an anharmonic spectrum of the circuit. The Josephson tunnel junction is a very thin superconductor-insulator-superconductor barrier that permits tunneling of the superconducting wave function across it. In engineering language, it behaves as a nonlinear inductor.

Superconducting flux qubit, consisting of a ring interrupted by 4 Josephson junctions. The circuit is made out of aluminum. The qubit measures 4um x 6um.

Superconducting qubits are obtained out of two of the states of the Josephson circuit nonlinear spectrum. There exist different types of superconducting qubits depending on whether the Josephson energy stored in the junction dominates over the capacitive energy. The most widely used qubits are the persistent current flux qubit and the Cooper pair box transmon qubit.

Superconducting qubits coupled to resonators are the on-chip analogue of single atoms coupled to single photons in a cavity, in the microwave regime of energies. In atom-photon cavity QED, the highest couplings achieved are 10-6 times smaller than the cavity frequency, while superconducting qubits can easily attain 10-2, entering regimes where unexplored physics take place. A nice and complete review of quantum optics with superconducting qubits can be found here.