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.

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!

 

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.

Happy birthday QUANTIC!

The QUANTIC group gathered last week to celebrate its first year of existence. A lot has been achieved and a lot needs to be done. Year 2 will bring lots of interesting times and lots of entangled qubits. Stay tuned!

Alba Cevera-Lierta awarded IBM ‘Teach me QISKit’

We are very happy to announce that our PhD student Alba Cervera-Lierta has won the IBM Q “Teach me QISKit’ by IBM” award! The contest was about writing and programming an interactive self-paced Jupyter Notebook tutorial that explained a specific focus topic in quantum computing using QISKit and the IBM Q Experience.
QISKit is an open quantum software developer toolkit provided by IBM Q to program quantum algorithms, both using a simulator or on one of their quantum devices.
Alba has programmed a quantum circuit that diagonalizes exactly the one-dimensional transverse Ising model. This model shows a quantum phase transition when the transverse magnetization reaches a critical point. At that point, the expected value of magnetization jumps due to the paramagnetic-ferromagnetic spin transition.
The quantum circuit, first proposed by Vestraete, Cirac and Latorre in 2008, has potential interests in condensed matter physics as it allows the exact simulation of all energy spectrum. Thus, other interesting simulations could be performed: for instance, Alba presented the time evolution of the state with all spins aligned, which shows an oscillation in the magnetization.
Finally, we just want to congratulate our collaborator for a job well done!
Enhorabona Alba!

 

QUANTIC group turns 1

Exactly a year ago, on June 1st 2017, we embarked in this adventure starting from a shared office at UB. We have gone a long way. Our team has grown in size, we have become a reference group for the community, we organized local and international events, we published relevant works in quantum computing and quantum optics, and we have an experiment about to be launched with one of the many collaborators we consolidated. But we are just getting started.

The coming year is going to consolidate our efforts theoretically and experimentally. We will show the first functional superconducting qubit in the south of Europe, new algorithms… but let’s not get ahead of the most important moment: the present. We have big news to celebrate (see next post), while we prepare the first experimental Benasque summer school and a lot more to come! Stay tuned!