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Author: Subject: Claimed quantum computer breakthough
MadHatter
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[*] posted on 6-12-2020 at 17:11
Claimed quantum computer breakthough


https://www.wired.com/story/china-stakes-claim-quantum-supre...
Food for thought. I don't know whether to believe it or not.




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clearly_not_atara
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[*] posted on 6-12-2020 at 17:18


Supposedly a reanalysis is being done with results expected in days to weeks. I'm pretty busy right now so I see no reason to speculate; I'll let them hash it out.



[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 7-12-2020 at 07:48


So when are the current encryption standards at stake?
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MadHatter
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[*] posted on 8-12-2020 at 18:46
Safety


https://arstechnica.com/science/2020/12/un-computable-quantu...
Just when you thought it was safe to explore anything.




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leau
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[*] posted on 5-12-2021 at 15:51


Connecting heterogeneous quantum networks by hybrid entanglement swapping

Giovanni Guccione, Tom Darras, Hanna Le Jeannic, Varun B. Verma, Sae Woo Nam, Adrien Cavaillès & Julien Laurat

Guccione et al., Sci. Adv. 2020; 6 : eaba4508 29 May 2020

Recent advances in quantum technologies are rapidly stimulating the building of quantum networks. With the parallel development of multiple physical platforms and different types of encodings, a challenge for present and future networks is to uphold a heterogeneous structure for full functionality and therefore support modular systems that are not necessarily compatible with one another. Central to this endeavor is the capability to distribute and interconnect optical entangled states relying on different discrete and continuous quantum variables. Here, we report an entanglement swapping protocol connecting such entangled states. We generate single-photon entanglement and hybrid entanglement between particle- and wave-like optical qubits and then demonstrate the heralded creation of hybrid entanglement at a distance by using a specific Bell-state measurement. This ability opens up the prospect of connecting heterogeneous nodes of a network, with the promise of increased integration and novel functionalities


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draculic acid69
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[*] posted on 5-12-2021 at 21:33


Quote: Originally posted by Fyndium  
So when are the current encryption standards at stake?


Now.or maybe soon. I wouldn't count on anything being unbreakable these days.
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[*] posted on 6-12-2021 at 10:51


Teleportation Systems Toward a Quantum Internet

Raju Valivarthi, Samantha I. Davis, Cristián Peña, Si Xie , Nikolai Lauk, Lautaro Narváez, Jason P. Allmaras, Andrew D. Beyer, Yewon Gim, Meraj Hussein, George Iskander , Hyunseong Linus Kim, Boris Korzh, Andrew Mueller, Mandy Rominsky, Matthew Shaw, Dawn Tang , Emma E. Wollman, Christoph Simon, Panagiotis Spentzouris, Daniel Oblak, Neil Sinclair and Maria Spiropulu

PRX QUANTUM 1, 020317 (2020) DOI: 10.1103/PRXQuantum.1.020317

Quantum teleportation is essential for many quantum information technologies, including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single-photon detectors and off-the-shelf optics, we achieve conditional quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of ≥ 90% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum Internet with practical devices.


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macckone
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[*] posted on 6-12-2021 at 11:00


For reference purposes you need at minimum the number of qubits in a number to factor it.

They are at 50-60 qubits and RSA encryption is currently using 4096 bits for long duration keys and 2048 for normal use keys.
There is a good ways to go.
The NSA has recommended against ECC for a while now, so my guess is they have a shortcut for ECC at least with some curves.
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[*] posted on 7-12-2021 at 13:20


How to profit from quantum technology without building quantum computers

Dmitry Green, Henning Soller, Yuval Oreg and Victor Galitski

www.nature.com/natrevphys
150 | March 2021 | volume 3

There are a number of lower risk opportunities to invest in quantum technologies, other than quantum computers, but to make the most of them both specialist knowledge and market awareness are required.


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[*] posted on 8-12-2021 at 08:33


Experimental Fock-state bunching capability of non-ideal single-photon states

Petr Zapletal, Tom Darras, Hanna Le Jeannic, Adrien Cavaillès, Giovanni Guccione, Julien Laurat & Radim Filip

Vol. 8, No. 5 / May 2021 / Optica

Advanced quantum technologies, as well as fundamental tests of quantum physics, crucially require the interferenceof multiple single photons in linear-optics circuits. This interference can result in the bunching of photons into higher Fock states, leading to a complex bosonic behavior. These challenging tasks timely require to develop collective criteria to benchmark many independent initial resources. Here we determine whether n independent imperfect single photons can ultimately bunch into the Fock state |ni. We thereby introduce an experimental Fock-state bunching capability for single-photon sources, which uses phase-space interference for extreme bunching events as a quantifier. In contrast to autocorrelation functions, this operational approach takes into account not only residual multi-photon components but also a vacuum admixture and the dispersion of individual photon statistics. We apply this approach to high-purity single photons generated from an optical parametric oscillator and show that they can lead to a Fock-state capability of at least 14. Our work demonstrates a novel collective benchmark for single-photon sources and their use in subsequent stringent applications.


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[*] posted on 9-12-2021 at 07:44


Validating multi-photon quantum interference with finite data


Quantum Sci. Technol. 5 (2020) 045005

https://doi.org/10.1088/2058-9565/aba03a

Fulvio Flamini, Mattia Walschaers, Nicolò Spagnolo, Nathan Wiebe, Andreas Buchleitner and Fabio Sciarrino

Multi-particle interference is a key resource for quantum information processing, as exemplified by Boson Sampling. Hence, given its fragile nature, an essential desideratum is a solid and reliable framework for its validation. However, while several protocols have been introduced to this end,the approach is still fragmented and fails to build a big picture for future developments. In this work, we propose an operational approach to validation that encompasses and strengthens the state of the art for these protocols. To this end, we consider the Bayesian hypothesis testing and the statistical benchmark as most favorable protocols for small- and large-scale applications, respectively. We numerically investigate their operation with finite sample size, extending previous tests to larger dimensions, and against two adversarial algorithms for classical simulation: the mean-field sampler and the metropolized independent sampler. To evidence the actual need for refined validation techniques, we show how the assessment of numerically simulated data depends on the available sample size, as well as on the internal hyper-parameters and other practically relevant constraints. Our analyses provide general insights into the challenge of validation, and can inspire the design of algorithms with a measurable quantum advantage.


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[*] posted on 10-12-2021 at 09:37


Teleportation Systems Toward a Quantum Internet

Raju Valivarthi, Samantha I. Davis, Cristián Peña, Si Xie, Nikolai Lauk, Lautaro Narváez, Jason P. Allmaras, Andrew D. Beyer, Yewon Gim, Meraj Hussein, George Iskander, Hyunseong Linus Kim, Boris Korzh, Andrew Mueller, Mandy Rominsky, Matthew Shaw, Dawn Tang, Emma E. Wollman, Christoph Simon, Panagiotis Spentzouris, Daniel Oblak, Neil Sinclair and Maria Spiropulu

PRX QUANTUM 1, 020317 (2020)
DOI: 10.1103/PRXQuantum.1.020317

Quantum teleportation is essential for many quantum information technologies, including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single-photon detectors and off-the-shelf optics, we achieve conditional quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of ≥ 90% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum Internet with practical devices.


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[*] posted on 11-12-2021 at 07:14


Efficient Quantum Teleportation of Unknown Qubit Based on DV-CV Interaction Mechanism

Sergey A. Podoshvedov

Entropy 2019, 21, 150; doi:10.3390/e21020150

We propose and develop the theory of quantum teleportation of an unknown qubit based on the interaction mechanism between discrete-variable (DV) and continuous-variable (CV) states on highly transmissive beam splitter (HTBS). This DV-CV interaction mechanism is based on the simultaneous displacement of the DV state on equal in absolute value, but opposite in sign displacement amplitudes by coherent components of the hybrid in such a way that all the information about the displacement amplitudes is lost with subsequent registration of photons in the auxiliary modes. The relative phase of the displaced unknown qubit in the measurement number state basis can vary on opposite, depending on the parity of the basis states in the case of the negative amplitude of displacement that is akin to action of nonlinear effect on the teleported qubit. All measurement outcomes of the quantum teleportation are distinguishable, but the teleported state at Bob’s disposal may acquire a predetermined amplitude-distorting factor. Two methods of getting rid of the factors are considered. The quantum teleportation is considered in various interpretations. A method for increasing the efficiency of quantum teleportation of an unknown qubit is proposed.


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[*] posted on 12-12-2021 at 07:54


Scheme for the generation of hybrid entanglement between time-bin and wavelike encodings

Élie Gouzien, Floriane Brunel, Sébastien Tanzilli, and Virginia D’Auria

Phys. Rev. A 102, 012603 – Published 2 July 2020
DOI:https://doi.org/10.1103/PhysRevA.102.012603

We propose a scheme for the generation of hybrid states entangling a single-photon time-bin qubit with a coherent-state qubit encoded on phases. Compared to other reported solutions, time-bin encoding makes hybrid entanglement particularly well adapted to applications involving long-distance propagation in optical fibers. This makes our proposal a promising resource for future out of-the-laboratory quantum communication. In this perspective, we analyze our scheme by taking into account realistic experimental resources and discuss the impact of their imperfections on the quality of the obtained hybrid state.


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[*] posted on 13-12-2021 at 10:32


Small quantum computers and large classical data sets

Aram W. Harrow

https://arxiv.org/abs/2004.00026

We introduce hybrid classical-quantum algorithms for problems involving a large classical data set X and a space of models Y such that a quantum computer has superposition access to Y but not X. These algorithms use data reduction techniques to construct a weighted subset of X called a coreset that yields approximately the same loss for each model. The coreset can be constructed by the classical computer alone, or via an interactive protocol in which the outputs of the quantum computer are used to help decide which elements of X to use. By using the quantum computer to perform Grover search or rejection sampling, this yields quantum speedups for maximum likelihood estimation, Bayesian inference and saddle-point optimization. Concrete applications include k-means clustering, logistical regression, zero-sum games and boosting.


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[*] posted on 14-12-2021 at 07:57


Highly photon loss tolerant quantum computing using hybrid qubits

S. Omkar, Y. S. Teo, Seung-Woo Lee, and H. Jeong

doi:10.1103/PhysRevA.103.032602 arXiv:2011.04209

We investigate a scheme for topological quantum computing using optical hybrid qubits and make an extensive comparison with previous all-optical schemes. We show that the photon loss threshold reported by Omkar et al. [Phys. Rev. Lett. 125, 060501 (2020)] can be improved further by employing postselection and multi-Bell-state-measurement based entangling operation to create a special cluster state, known as Raussendorf lattice for topological quantum computation. In particular, the photon loss threshold is enhanced up to 5.7 × 10 −3 , which is the highest reported value given a reasonable error model. This improvement is obtained at the price of consuming more resources by an order of magnitude, compared to the scheme in the aforementioned reference. Neverthless, this scheme remains resource-efficient compared to other known optical schemes for fault-tolerant quantum computation.


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[*] posted on 15-12-2021 at 05:44


Quantum Spin Liquid States

Yi Zhou, Kazushi Kanoda, Tai-Kai Ng

Rev. Mod. Phys. 89, 025003 (2017) DOI: 10.1103/RevModPhys.89.025003

This article is an introductory review of the physics of quantum spin liquid (QSL) states. Quantum magnetism is a rapidly evolving field, and recent developments reveal that the ground states and low-energy physics of frustrated spin systems may develop many exotic behaviors once we leave the regime of semi-classical approaches. The purpose of this article is to introduce these developments. The article begins by explaining how semi-classical approaches fail once quantum mechanics become important and then describes the alternative approaches for addressing the problem. We discuss mainly spin 1/2 systems, and we spend most of our time in this article on one particular set of plausible spin liquid states in which spins are represented by fermions. These states are spin-singlet states and may be viewed as an extension of Fermi liquid states to Mott insulators, and they are usually classified in the category of so-called SU (2), U (1) or Z 2 spin liquid states. We review the basic theory regarding these states and the extensions of these states to include the effect of spin-orbit coupling and to higher spin (S > 1/2) systems. Two other important approaches with strong influences on the understanding of spin liquid states are also introduced: (i) matrix product states and projected entangled pair states and (ii) the Kitaev honeycomb model. Experimental progress concerning spin liquid states in realistic materials, including anisotropic triangular lattice systems (κ-(ET) 2 Cu 2 (CN) 3 and EtMe 3 Sb[(Pd(dmit) 2 ] 2 ), kagome lattice systems (ZnCu 3 (OH) 6 Cl 2 ) and hyperkagome lattice systems (Na 4 Ir 3 O 8 ), is reviewed and compared against the corresponding theories.


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[*] posted on 16-12-2021 at 09:52


Probing Topological Spin Liquids on a Programmable Quantum Simulator

G. Semeghini, H. Levine, A. Keesling, S. Ebadi, T. T. Wang, D. Bluvstein , R. Verresen, H. Pichler M. Kalinowski, R. Samajdar, A. Omran, S. Sachdev , A. Vishwanath , M. Greiner, V. Vuletić , M. D. Lukin

DOI: 10.1126/science.abi8794
https://arxiv.org/pdf/2104.04119

Quantum spin liquids, exotic phases of matter with topological order, have been a major focus of explorations in physical science for the past several decades. Such phases feature long-range quantum entanglement that can potentially be exploited to realize robust quantum computation. We use a 219-atom programmable quantum simulator to probe quantum spin liquid states. In our approach, arrays of atoms are placed on the links of a kagome lattice and evolution under Rydberg blockade creates frustrated quantum states with no local order. The onset of a quantum spin liquid phase of the paradigmatic toric code type is detected by evaluating topological string operators that provide direct signatures of topological order and quantum correlations. Its properties are further revealed by using an atom array with nontrivial topology, representing a first step towards topological encoding. Our observations enable the controlled experimental exploration of topological quantum matter and protected quantum information processing.


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[*] posted on 17-12-2021 at 07:08


Supplementary Materials for Probing topological spin liquids on a programmable quantum simulator

G. Semeghini et al.

Science 374, 1242 (2021) DOI: 10.1126/science.abi8794


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[*] posted on 22-12-2021 at 08:37


Quantum Teleportation Between Discrete and Continuous Encodings of an Optical Qubit

Alexander E. Ulanov, Demid Sychev, Anastasia A. Pushkina, Ilya A. Fedorov, and A. I. Lvovsky

DOI: 10.1103/PhysRevLett.118.160501

The transfer of quantum information between physical systems of a different nature is a central matter in quantum technologies. Particularly challenging is the transfer between discrete and continuous degrees of freedom of various harmonic oscillator systems. Here we implement a protocol for teleporting a continuous-variable optical qubit, encoded by means of low-amplitude coherent states, onto a discrete-variable, single-rail qubit—a superposition of the vacuum and single-photon optical states—via a hybrid entangled resource we test our protocol on a one-dimensional manifold of the input qubit space and demonstrate the mappingonto the equator of the teleported qubit’s Bloch sphere with an average fidelity of 0.83 - 0.04. Our work opens up the way to the wide application of quantum information processing techniques where discrete- and continuous-variable encodings are combined within the same optical circuit.


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[*] posted on 23-12-2021 at 07:43


Hybrid entanglement between optical discrete polarizations and continuous quadrature variables

Jianming Wen, Irina Novikova, Chen Qian, Chuanwei Zhang and Shengwang Du


https://arxiv.org/abs/2105.04602

By coherently combining advantages while largely avoiding limitations of two mainstream platforms, optical hybrid entanglement involving both discrete and continuous variables has recently garnered widespread attention and emerged as a promising idea for building heterogenous quantum networks. Different from previous results, here we propose a new scheme to remotely generate hybrid entanglement between discrete-polarization and continuous-quadrature optical qubits heralded by two-photon Bell state measurement. As a novel nonclassical light resource, we further utilize it to discuss two examples of ways – entanglement swapping and quantum teloportation – in which quantum information processing and communications could make use of this hybrid technique.


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[*] posted on 24-12-2021 at 06:13


Quantum Ising Hamiltonian Programming in Trio, Quartet, and Sextet Qubit Systems

Minhyuk Kim, Yunheung Song, Jaewan Kim and Jaewook Ahn



PRX QUANTUM 1, 020323 (2020)
DOI: 10.1103/PRXQuantum.1.020323

Rydberg-atom quantum simulators are of keen interest because of their possibilities towards high-dimensional qubit architectures. Here we report continuous tuning of quantum Ising Hamiltonians of Rydberg atoms in three-dimensional arrangements. Various connected graphs of Rydberg atoms constructed with vertices and edges respectively representing atoms and Rydberg-blockaded atom pairs, and their eigenenergies are probed along with their geometric intermediates during structural transformations.Conformation spectra of star, complete, cyclic, and diamond graphs are probed for four interacting atoms and antiprism structures for six atoms. The energy level shifts and merges of the tested structural transformations are clearly observed with Fourier-transform spectroscopy, in good agreement with the model few-body quantum Ising Hamiltonian. This result demonstrates the possibility of continuous geometry tuning and thus programming of many-body spin-Hamiltonian systems.


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[*] posted on 25-12-2021 at 07:48


Observing crossover between quantum speed limits

Gal Ness, Manolo R. Lam, Wolfgang Alt, Dieter Meschede, Yoav Sagi & Andrea Alberti

Sci. Adv. 7, eabj9119 (2021)
DOI: 10.1126/sciadv.abj9119

Quantum mechanics sets fundamental limits on how fast quantum states can be transformed in time. Two well-known quantum speed limits are the Mandelstam-Tamm and the Margolus-Levitin bounds, which relate the maximum speed of evolution to the system’s energy uncertainty and mean energy, respectively. Here, we test concurrently both limits in a multilevel system by following the motion of a single atom in an optical trap using fast matter wave interferometry. We find two different regimes: one where the Mandelstam-Tamm limit constrains the evolution at all times, and a second where a crossover to the Margolus-Levitin limit occurs at longer times. We take a geometric approach to quantify the deviation from the speed limit, measuring how much the quantum evolution deviates from the geodesic path in the Hilbert space of the multilevel system. Our results are important to understand the ultimate performance of quantum computing devices and related advanced quantum technologies.


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[*] posted on 26-12-2021 at 08:05


Resonance from antiferromagnetic spin fluctuations for superconductivity in UTe 2

Chunruo Duan, R. E. Baumbach, Andrey Podlesnyak, Yuhang Deng, Camilla Moir, Alexander J. Breindel, M. Brian Maple, E. M. Nica, Qimiao Si and Pengcheng Dai

DOI: 10.1038/s41586-021-04151-5
https://arxiv.org/abs/2106.14424

Superconductivity has its universal origin in the formation of bound (Cooper) pairs of electrons that can move through the lattice without resistance below the superconducting transition temperature Tc. While electron Cooper pairs in most superconductors form anti-parallel spin-singlets with total spin S=0, they can also form parallel spin-triplet Cooper pairs with S=1 and an odd parity wavefunction, analogous to the equal spin pairing state in the superfluid 3He. Spin-triplet pairing is important because it can host topological states and Majorana fermions relevant for fault tolerant quantum computation. However, spin-triplet pairing is rare and has not been unambiguously identified in any solid state systems. Since spin-triplet pairing is usually mediated by ferromagnetic (FM) spin fluctuations, uranium based heavy-fermion materials near a FM instability are considered ideal candidates for realizing spin-triplet superconductivity. Indeed, UTe2, which has a Tc=1.6K, has been identified as a strong candidate for chiral spin-triplet topological superconductor near a FM instability, although the system also exhibits antiferromagnetic (AF) spin fluctuations]. Here we use inelastic neutron scattering (INS) to show that superconductivity in UTe2 is coupled with a sharp magnetic excitation at the Brillouin zone (BZ) boundary near AF order, analogous to the resonance seen in high-Tc copper oxide, iron-based, and heavy-fermion superconductors. We find that the resonance in UTe2 occurs below Tc at an energy Er=7.9kBTc (kB is Boltzmann's constant) and at the expense of low-energy spin fluctuations. Since the resonance has only been found in spin-singlet superconductors near an AF instability, its discovery in UTe2 suggests that AF spin fluctuations can also induce spin-triplet pairing for superconductivity.


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[*] posted on 27-12-2021 at 08:10


Real-Time Error Correction for Quantum Computing Philip Ball Physics 14, 184 | DOI: 10.1103/Physics.14.184 Random errors incurred during computation are one of the biggest obstacles to unleashing the full power of quantum computers. Researchers have now demonstrated a technique that allows errors to be detected and corrected in real time as the computation proceeds. It also allows error correction to be conducted several times on a single quantum bit (qubit) during the calculation. Both features are needed to make the basic elements—the logical qubits—of a fully error-tolerant quantum computer that can be scaled up and used for applications beyond the specialized ones that these machines have tackled so far.

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