Show threadRafael WagnerOct 12, 2023

One by-product that may be of independent interest, we prescribe examples of quantum realizable logically contextual behaviours for all n-cycle scenario's in an elegant and unified manner!

Thanks to #FCT_Portugal for the funding and #INL #QLOC_INL for the healthy and engaging environment for visitors!

Rafael WagnerOct 12, 2023

After a #QLOC_talk and some workouts in the calisthenics park near INL, a fresh #arXiv #preprint is out!! https://arxiv.org/abs/2310.06976

First e-print with
Laurens Walleghem
that was visiting us at #QLOC_INL this year, and the first of his PhD! (Congrats!)

Extended Wigner's friend paradoxes do not require nonlocal correlations

Extended Wigner's friend no-go theorems provide a modern lens for investigating the measurement problem, by making precise the challenges that arise when one attempts to model agents as dynamical quantum systems. Most such no-go theorems studied to date, such as the Frauchiger-Renner argument and the Local Friendliness argument, are explicitly constructed using quantum correlations that violate Bell inequalities. In this work, we show that such correlations are not necessary for having extended Wigner's friend paradoxes, by constructing a no-go theorem utilizing a proof of the failure of noncontextuality. The argument hinges on a novel metaphysical assumption (which we term Commutation Irrelevance) that is a natural extension of a key assumption going into the Frauchiger and Renner's no-go theorem.

arXiv.org
Rafael WagnerOct 11, 2023

New #arXiv #preprint from the Quantum and Linear-Optical Computation group , at INL!! #QLOC_INL

https://arxiv.org/abs/2310.06034

By researcher Leonardo Novo!

In their new work they are investigating the complexity of computing transition probabilities of Gaussian processes.

Their proof stems from connecting it with the problem of Gaussian boson sampling, known to be hard.

A neat by-product is a #Hadamard_test for continuous-variable systems.

Complexity of Gaussian quantum optics with a limited number of non-linearities

It is well known in quantum optics that any process involving the preparation of a multimode gaussian state, followed by a gaussian operation and gaussian measurements, can be efficiently simulated by classical computers. Here, we provide evidence that computing transition amplitudes of Gaussian processes with a single-layer of non-linearities is hard for classical computers. To do so, we show how an efficient algorithm to solve this problem could be used to efficiently approximate outcome probabilities of a Gaussian boson sampling experiment. We also extend this complexity result to the problem of computing transition probabilities of Gaussian processes with two layers of non-linearities, by developing a Hadamard test for continuous-variable systems that may be of independent interest. Given recent experimental developments in the implementation of photon-photon interactions, our results may inspire new schemes showing quantum computational advantage or algorithmic applications of non-linear quantum optical systems realizable in the near-term.

arXiv.org
Rafael WagnerFeb 28, 2023

New #QLOC_INL#arXiv of PhD Student Filipa Peres!!!

Her prior work on #Pauli_Based_Quantum_Computation (PBC) on hybrid computation https://arxiv.org/abs/2203.01789, together with Ernesto Galvão, improved the cost of compilation and #hybrid_computation using PBC (with open source code for it!).

PBC so far used only qubit encoding, but #error_correction or photonic computation that encode information on #qudits are of great relevance. In her new work, she generalizes PBC to qudits! https://arxiv.org/abs/2302.13702

Quantum circuit compilation and hybrid computation using Pauli-based computation

Pauli-based computation (PBC) is driven by a sequence of adaptively chosen, non-destructive measurements of Pauli observables. Any quantum circuit written in terms of the Clifford+$T$ gate set and having $t$ $T$ gates can be compiled into a PBC on $t$ qubits. Here we propose practical ways of implementing PBC as adaptive quantum circuits and provide code to do the required classical side-processing. Our schemes reduce the number of quantum gates to $O(t^2)$ (from a previous $O(t^3 / \log t)$ scaling) and space/time trade-offs are discussed which lead to a reduction of the depth from $O(t \log t)$ to $O(t)$ within our schemes, at the cost of $t$ additional auxiliary qubits. We compile examples of random and hidden-shift quantum circuits into adaptive PBC circuits. We also simulate hybrid quantum computation, where a classical computer effectively extends the working memory of a small quantum computer by $k$ virtual qubits, at a cost exponential in $k$. Our results demonstrate the practical advantage of PBC techniques for circuit compilation and hybrid computation.

arXiv.org
Rafael WagnerFeb 22, 2023

#QLOC_INL #JournalClub #Ulm

The PhD student José Diogo Guimarães, in a joint work with collaborators from #UniversityUlm and #UniversityMinho, explained novel results on simulating open quantum sistems with NISQ devices by applying error mitigation in order to have control over the effect Lindblad evolution of the quantum computer.

Super awesome results. Congratulations José for these advancements!

Rafael WagnerJan 10, 2023

A new paper from my research group at #INL on #BosonSampling!!

New #QLOC_INL publication! Joint work by my supervisor Ernesto Galvão with Fabio Sciarrino, Nicolò Spagnolo (Rome) and Daniel Brod (UFF).

https://www.nature.com/articles/s41534-023-00676-x

Here they explore how to simulate non-linear photonic gates using linear optics, as a way to gauge the associated complexity. In particular, they look at simulations of non-linear phase gates, and how the complexity is affected by the density of photons in the device.

Non-linear Boson Sampling - npj Quantum Information

Boson Sampling is a task that is conjectured to be computationally hard for a classical computer, but which can be efficiently solved by linear-optical interferometers with Fock state inputs. Significant advances have been reported in the last few years, with demonstrations of small- and medium-scale devices, as well as implementations of variants such as Gaussian Boson Sampling. Besides the relevance of this class of computational models in the quest for unambiguous experimental demonstrations of quantum advantage, recent results have also proposed the first applications for hybrid quantum computing. Here, we introduce the adoption of non-linear photon–photon interactions in the Boson Sampling framework, and analyze the enhancement in complexity via an explicit linear-optical simulation scheme. By extending the computational expressivity of Boson Sampling, the introduction of non-linearities promises to disclose novel functionalities for this class of quantum devices. Hence, our results are expected to lead to new applications of near-term, restricted photonic quantum computers.

Nature
Rafael WagnerDec 20, 2022

#BosonSampling is a problem that has hardness of classical simulation well established, but that quantum systems can do absurdly fast

One major difficulty is that this sampling task is not easy to be verified, hence not clear how to benchmark #QuantumAdvantage BosonSampling experiments

In a new preprint from #QLOC_INL Leonardo Novo, together with Benoît Seron (main author), A Arkhipov and N Cerf advance the field of Boson Sampling validation!
https://scirate.com/arxiv/2212.09643

Congrats to Benoît et al!

Efficient validation of Boson Sampling from binned photon-number distributions

In order to substantiate claims of quantum computational advantage, it is crucial to develop efficient methods for validating the experimental data. We propose a test of the correct functioning of a boson sampler with single-photon inputs that is based on how photons distribute among partitions of the output modes. Our method is versatile and encompasses previous validation tests based on bunching phenomena, marginal distributions, and even some suppression laws. We show via theoretical arguments and numerical simulations that binned-mode photon number distributions can be used in practical scenarios to efficiently distinguish ideal boson samplers from those affected by realistic imperfections, especially partial distinguishability of the photons.

SciRate
Rafael WagnerDec 8, 2022

New #QLOC_INL preprint out!! https://scirate.com/arxiv/2212.03668!!!!!

PhD Student Michael together with PI's Ernesto Galvão and Luis Barbosa study quantum advantages in a restricted version of MQBC (non-adaptive) when computing Boolean functions!

This is one result among others that push us to better understand the connections/differences between adaptive/non-adaptive quantum computation.

Quantum advantage in temporally flat measurement-based quantum computation

Several classes of quantum circuits have been shown to provide a quantum computational advantage under certain assumptions. The study of ever more restricted classes of quantum circuits capable of quantum advantage is motivated by possible simplifications in experimental demonstrations. In this paper we study the efficiency of measurement-based quantum computation with a completely flat temporal ordering of measurements. We propose new constructions for the deterministic computation of arbitrary Boolean functions, drawing on correlations present in multi-qubit Greenberger, Horne, and Zeilinger (GHZ) states. We characterize the necessary measurement complexity using the Clifford hierarchy, and also generally decrease the number of qubits needed with respect to previous constructions. In particular, we identify a family of Boolean functions for which deterministic evaluation using non-adaptive MBQC is possible, featuring quantum advantage in width and number of gates with respect to classical circuits.

SciRate