Descubriendo el potencial de la computación cuántica

@article{nokey,

title = {Superadditivity effects of quantum capacity decrease with the dimension for qudit depolarizing channels},

author = {Etxezarreta Martinez, J. and deMarti iOlius, A. and Crespo, P. M. },

url = {https://quantumspain-project.es/wp-content/uploads/2023/10/2301.10132-2.pdf},

doi = {doi.org/10.48550/arXiv.2301.10132},

year  = {2023},

date = {2023-09-12},

urldate = {2023-09-12},

journal = {Physical Review A},

volume = {108},

issue = {3},

abstract = {Quantum channel capacity is a fundamental quantity in order to understand how well quantum information can be transmitted or corrected when subjected to noise. However, it is generally not known how to compute such quantities since the quantum channel coherent information is not additive for all channels, implying that it must be maximized over an unbounded number of channel uses. This leads to the phenomenon known as superadditivity, which refers to the fact that the regularized coherent information of n channel uses exceeds one-shot coherent information. In this article, we study how the gain in quantum capacity of qudit depolarizing channels relates to the dimension of the considered systems. We make use of an argument based on the no-cloning bound in order to prove that the possible superadditive effects decrease as a function of the dimension for such family of channels. In addition, we prove that the capacity of the qudit depolarizing channel coincides with the coherent information when d→∞. We also discuss the private classical capacity and obtain similar results. We conclude that when high-dimensional qudits experiencing depolarizing noise are considered, the coherent information of the channel is not only an achievable rate, but essentially the maximum possible rate for any quantum block code.},

keywords = {tecnun},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Performance enhancement of surface codes via recursive minimum-weight perfect-match decoding},

author = {De Marti i Olius, A. and Etxezarreta Martinez, J. and Fuentes, P. and Crespo, P. M.},

url = {https://quantumspain-project.es/wp-content/uploads/2023/10/2212.11632.pdf},

doi = {doi.org/10.1103/PhysRevA.108.022401},

isbn = {2469-9934},

year  = {2023},

date = {2023-08-03},

urldate = {2023-08-03},

journal = {Physical Review A},

volume = {108},

issue = {2},

abstract = {The minimum weight perfect matching (MWPM) decoder is the standard decoding strategy for quantum surface codes. However, it suffers a harsh decrease in performance when subjected to biased or nonidentical quantum noise. In this work, we modify the conventional MWPM decoder so that it considers the biases, the nonuniformities, and the relationship between X, Y, and Z errors of the constituent qubits of a given surface code. Our modified approach, which we refer to as the recursive MWPM decoder, obtains an 18% improvement in the probability threshold pth under depolarizing noise. We also obtain significant performance improvements when considering biased noise and independent nonidentically distributed (i.ni.d.) error models derived from measurements performed on state-of-the-art quantum processors. In fact, when subjected to i.ni.d. noise, the recursive MWPM decoder yields a performance improvement of 105.5%  over the conventional MWPM strategy, and in some cases, it even surpasses the performance obtained over the well-known depolarizing channel.},

keywords = {tecnun},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Multiqubit time-varying quantum channels for NISQ-era superconducting quantum processors},

author = {Etxezarreta Martinez, J. and Fuentes, P. and De Marti i Olius, A. and Garcia-Frias, J. and Rodriguez Fonollosa, J. and Crespo, P. M. },

url = {https://quantumspain-project.es/wp-content/uploads/2023/10/PhysRevResearch.5.033055.pdf},

doi = {doi.org/10.1103/PhysRevResearch.5.033055},

isbn = {2643-1564},

year  = {2023},

date = {2023-07-23},

urldate = {2023-07-23},

journal = {Physical Review Research},

volume = {5},

abstract = {Time-varying quantum channels (TVQCs) have been proposed as a model to include fluctuations of the relaxation (T1) and dephasing times (T2). In previous works, realizations of multiqubit TVQCs have been assumed to be equal for all the qubits of an error correction block, implying that the random variables that describe the fluctuations of T1 and T2 are block-to-block uncorrelated but qubit-wise perfectly correlated for the same block. In this article, we perform a correlation analysis of the fluctuations of the relaxation times of five multiqubit quantum processors. Our results show that it is reasonable to assume that the fluctuations of the relaxation and dephasing times of superconducting qubits are local to each of the qubits of the system. Based on these results, we discuss the multiqubit TVQCs when the fluctuations of the decoherence parameters for an error correction block are qubit-wise uncorrelated (as well as from block-to-block), a scenario we have named the fast time-varying quantum channel (FTVQC). Furthermore, we lower-bound the quantum capacity of general FTVQCs based on a quantity we refer to as the ergodic quantum capacity. Finally, we use numerical simulations to study the performance of quantum error correction codes when they operate over FTVQCs.},

keywords = {tecnun},

pubstate = {published},

tppubtype = {article}

}