First experimental PhD student!

The Quantic team has a new addition: David López Núñez. He is going to be the first experimental PhD student of the Quantic group. He obtained his Bachelor Degree in Physics at Universitat de Barcelona. There, he also studied a Master’s Degree in Advanced Physics. He now moved towards experiments and is currently pursuing a PhD on quantum computing with superconducting circuits.

Welcome David!

New publication by Alba Cervera-Lierta and José Ignacio Latorre

Quantic PhD student Alba Cervera-Lierta and our P.I. José Ignacio Latorre have published a new article on Journal of Physics A: Mathematical and Theoretical.

The article title is “Multipartite entanglement in spin chains and the hyperdeterminant” and the reference is J. Phys. A: Math. Theor. 51 505301 (2018) (arXiv: [quant-ph] 1802.02596).

In this work, they study the multipartite entanglement in spin chains, in particular in the Ising model, XXZ model and Haldane-Shastry model.

As a figure of merit to quantify multipartite entanglement they use the Cayley hyperdeterminant, which is a polynomial constructed with the components of the wave function which is invariant under local unitary transformation. For n=2 and n=3, the hyperdeterminant coincides with the concurrence and the tangle respectively, well known figures of merit for multipartite entanglement. For n=4, Hyperdeterminant is a polynomial of degree 24 that can be written in terms of more simple polynomials, S and T, of degree 8 and 12 respectively.

They observe that these polynomials are able to capture the phase transitions present in the models studied as well as a subclass of quadripartite entanglement present in the eigenstates.

Besides spin chains, they also study the quadripartite entanglement of random states, ground states of random matrix Hamiltonians in the Wigner-Syson Gaussian ensambles and the quadripartite entangled states defined by Vestraete et al in 2002.

This figure shows the hyperdeterminant for the ground state and second excited state of a n=4 Ising spin chain as a function of the transverse magnetic field λ. For an infinite chain, this model has a phase transition at λ=1. As can be seen, the hyperdeterminant peaks close to this phase transition.

Seth Lloyd (MIT) visited us

A few days ago we were very honored to receive one of the top names in the world in Quantum Information such as Prof. Seth Lloyd from the Massachusetts Institute of Technology. Prof. Lloyd gave a seminar at the Physics Department at UB where he described his recent progress in Quantum Machine Learning, a field where he has been focusing lately, being one of the most promising to achieve quantum advantages in real-life applications in a not-so-distant future.

Prof. Seth Lloyd has been one of the pioneers of the quantum information field for his theoretical work in quantum simulation and quantum computation, aside from being very close to experimentalists, as shown by his record of joint works in NMR, superconducting qubits, and photonics, among other experimental areas of quantum information. In recent years his group has also entered the surprising area of Quantum Biology, where work on quantum description of processes such as photosynthesis has been published with a very high impact.

The visit could not end with a tour at Mare Nostrum.

Researchers’ night 2018

Pol Forn-Díaz and Alba Cervera-Lierta have participated in European Researchers’ Night 2018 by giving a talk at Cosmocaixa, Barcelona.

They gave a microtalk which consisted on 8 minutes talk about some scientific topic explained to a general audience. First, Alba presented what is a quantum computer and what are its aplications: to study new chemical reactions, to solve optimization problems or to simulate quantum systems. Second, Pol explained how it works and what is the appearence of its building blocks, qubits. In particular, he showed how is our quantum processor made of superconducting qubits.

 

Quantic team members are very active in scientific outreach activities. Follow us on twitter to stay informed about future events!

 

Tim Menke from MIT visits us

Last week we had a distinguished guest for the whole week. Tim Menke from the MIT group of Engineering Quantum Systems visited us through the MIT-La Caixa Foundation project which Dr. Forn-Díaz has together with Prof. Will Oliver from MIT to develop new circuits for quantum annealing and allow students and PIs to spend short periods of time at MIT/BSC.

Tim’s work is focusing on reverse-engineering circuits by theoretically sampling circuits with different properties and selecting the ones that display a response close to the desired one. Then those circuits can be fabricated and tested in an experiment. Tim also performs measurements in the quantum annealing project within MIT.

Tim has helped us a lot in the lab work to get the qubit control electronics and software up and running. Thanks for the visit Tim!

New publication by Dr. Forn-Díaz

Dr. Forn-Díaz has participated in a joint work with the group of Prof. Chris Wilson at IQC Waterloo on the area of generation of entangled states of microwave generation, which has just been published to Physical Review Applied. The work, part of which was carried out during Pol’s postdoctoral position at Prof. Wilson’s lab, focuses on a nonlinear multimode resonator that generates entangled states of radiation by the application of external pumping fields at the suitable driving frequencies. The key aspect of the circuit is the presence of a SQUID at the end of the line which mediates the interaction between different modes. This work is very important for the generation of nonclassical states of microwave radiation, which are applicable in the area of quantum communication and quantum sensing.

The reference of the publication is Phys. Rev. Applied 10, 044019 (2018).

Cartoon of the superconducting resonator (top). In the middle, an optical microscope image of the region with the SQUID. At the bottom the lowest 3 modes are shown as function of the magnetic flux applied to the SQUID.

Carlos Bravo awarded grant Unitary fund

The Quantic team member Carlos Bravo has been recently awarded with a grant by the Unitary fund from Will Zeng, product lead for the forest experimental quantum programming toolkit at Rigetti Computing, who just started running his own quantum fund.

Carlos’s project will be based on the implementation of Adiabatically Assisted Variational Quantum Eigensolvers (AAVQE) in Forest (Rigetti’s quantum developer environment). This modern classical-quantum algorithm is an original idea from Dr. A. Garcia-Saez and Prof. J.I. Latorre from Quantic and is currently under review (arXiv:1806.02287). The AAVQE tackles optimization problems, with its basic idea being the assistance of variational quantum eigensolvers (VQE) with an adiabatic change of the Hamiltonian. The main problem that VQE algorithms face is in finding a reasonable path in the parameter space of the circuit to ending up in the correct solution. This problem may be solved by adiabatically evolving the Hamiltonian. Finally, Carlos is going to test AAVQE in order to solve hard classic and quantum problems.

Congratulations Carlos!

Sergi Ramos successfully defends his undergraduate project TFG at UB

Last July, BSC member Sergi Ramos defended his TFG (Treball de Final de Grau, the equivalent of a Bachelor’s thesis) titled ‘Gap analysis for an adiabatic approach to the Exact Cover problem’. Sergi received an outstanding score!

Here is a summary of the project:

Adiabatic quantum computation is widely used for solving satisfiability problems. One of this problems is the Exact Cover problem, an extension to the 3-SAT problem with a unique solution. This fact makes the adiabatic approach to quantum computation extremely useful when solving this Exact Cover problem, as one can map the unique solution to a non-degenerate energy ground state.

The time needed to perform a computation scales with the inverse of the gap energy, squared. This gap energy is the energy difference between the ground state, solution of the problem, and the first excited state. A way in which the computation time can be improves is by finding an algorithm that increases the gap energy of the problem.

The algorithm proposed is based on the idea that not all clauses of the problem affect the outcome in the same way. Using a weighted system that classifies each clause in the problem using their number of appearances in each different instance, an improvement in the gap energy has been found. Additionally, the gap gain increases with the number of clauses (qubits) in the problem, since their underlying symmetries can be exploited more easily.

Congratulations Sergi!!

Improvement provided by Sergi’s algorithm, seen as a higher slope towards large n than linear.

QUANTIC member Pol Forn-Díaz is interviewed at El Confidencial

The QUANTIC team keeps making noise in the media. Today, an article out of an interview by Dr. Pol Forn-Díaz has been published at El Confidencial. In the article, Pol describes with rather high accuracy the techniques used to fabricate devices, and explains with a dose of realism what building a quantum processor entails. The article also refers to Pol’s PhD advisor Prof. Mooij at TU Delft, as one of the fathers of one of the most important superconducting qubits, the flux qubit.

It is true Pol was the first in the country to learn about the fabrication and measurement techniques of superconducting qubits. By now he is not the only one, but he is one of the very few active and the only one leading an experimental team at a research institute such as BSC.

Pol posing in front of the ICN2 dilution fridge which is being wired up for the first superconducting qubit experiments in the country.