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Category: quantum physics – Page 404

Researchers use measurements to generate quantum entanglement and teleportation

Quantum mechanics is full of weird phenomena, but perhaps none as weird as the role measurement plays in the theory. Since a measurement tends to destroy the “quantumness” of a system, it seems to be the mysterious link between the quantum and classical world. And in a large system of quantum bits of information, known as “qubits,” the effect of measurements can induce dramatically new behavior, even driving the emergence of entirely new phases of quantum information.

This happens when two competing effects come to a head: interactions and measurement. In a quantum system, when the qubits interact with one another, their information becomes shared nonlocally in an “entangled state.” But if you measure the system, the is destroyed. The battle between measurement and interactions leads to two : one where interactions dominate and entanglement is widespread, and one where measurements dominate, and entanglement is suppressed.

As reported in the journal Nature, researchers at Google Quantum AI and Stanford University have observed the crossover between these two regimes—known as a “measurement-induced phase transition”—in a system of up to 70 qubits. This is by far the largest system in which measurement-induced effects have been explored.

Thirty Years Later, a Speed Boost for Quantum Factoring

As Shor looked for applications for his quantum period-finding algorithm, he rediscovered a previously known but obscure mathematical theorem: For every number, there exists a periodic function whose periods are related to the number’s prime factors. So if there’s a number you want to factor, you can compute the corresponding function and then solve the problem using period finding — “exactly what quantum computers are so good at,” Regev said.

On a classical computer, this would be an agonizingly slow way to factor a large number — slower even than trying every possible factor. But Shor’s method speeds up the process exponentially, making period finding an ideal way to construct a fast quantum factoring algorithm.

Shor’s algorithm was one of a few key early results that transformed quantum computing from an obscure subfield of theoretical computer science to the juggernaut it is today. But putting the algorithm into practice is a daunting task, because quantum computers are notoriously susceptible to errors: In addition to the qubits required to perform their computations, they need many others doing extra work to keep them from failing. A recent paper by Ekerå and the Google researcher Craig Gidney estimates that using Shor’s algorithm to factor a security-standard 2,048-bit number (about 600 digits long) would require a quantum computer with 20 million qubits. Today’s state-of-the-art machines have at most a few hundred.

Nonclassical Advantage in Metrology Established via Quantum Simulations of Hypothetical Closed Timelike Curves

We construct a metrology experiment in which the metrologist can sometimes amend the input state by simulating a closed timelike curve, a worldline that travels backward in time. The existence of closed timelike curves is hypothetical. Nevertheless, they can be simulated probabilistically by quantum-teleportation circuits. We leverage such simulations to pinpoint a counterintuitive nonclassical advantage achievable with entanglement. Our experiment echoes a common information-processing task: A metrologist must prepare probes to input into an unknown quantum interaction. The goal is to infer as much information per probe as possible. If the input is optimal, the information gained per probe can exceed any value achievable classically. The problem is that, only after the interaction does the metrologist learn which input would have been optimal.

Physicists create new form of antenna for radio waves

University of Otago physicists have used a small glass bulb containing an atomic vapor to demonstrate a new form of antenna for radio waves. The bulb was “wired up” with laser beams and could therefore be placed far from any receiver electronics.

Dr. Susi Otto, from the Dodd-Walls Center for Photonic and Quantum Technologies, led the field testing of the portable atomic radio sensor. A paper on the creation was published in Applied Physics Letters.

Such sensors, that are enabled by atoms in a so-called Rydberg state, can provide superior performance over current antenna technologies as they are highly sensitive, have broad tunability, and small physical size, making them attractive for use in defense and communications.

The A.I. Dilemma

Tristan Harris and Aza Raskin discuss how existing A.I. capabilities already pose catastrophic risks to a functional society, how A.I. companies are caught in a race to deploy as quickly as possible without adequate safety measures, and what it would mean to upgrade our institutions to a post-A.I. world.

This presentation is from a private gathering in San Francisco on March 9th, 2023 with leading technologists and decision-makers with the ability to influence the future of large-language model A.I.s. This presentation was given before the launch of GPT-4.

We encourage viewers to consider calling their political representatives to advocate for holding hearings on AI risk and creating adequate guardrails.

For the podcast version, please visit: https://www.humanetech.com/podcast/the-ai-dilemma.

Continue reading “The A.I. Dilemma” | >

The four types of planetary civilizations, explained by Michio Kaku

Humanity is a type 0 civilization. Here’s what types 1, 2, and 3 look like, according to physicist Michio Kaku.

Is anybody out there? Renowned physicist Michio Kaku discusses we could identify and categorize advanced extraterrestrial civilizations.

According to Kaku, while recognizing intelligence in space is challenging, Quantum computers may be able to help sift through data for signals of intelligence, similarly to how we analyze patterns in dolphin communication.

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Solving quantum mysteries: New insights into 2D semiconductor physics

Researchers from Monash University have unlocked fresh insights into the behavior of quantum impurities within materials.

The new, international theoretical study introduces a novel approach known as the “quantum virial expansion,” offering a powerful tool to uncover the complex quantum interactions in two-dimensional semiconductors.

This breakthrough holds potential to reshape our understanding of complex quantum systems and unlock exciting future applications utilizing novel 2D materials.

Thought experiments and conservation laws: Reevaluating quantum conservation principles

Conservation laws are central to our understanding of the universe, and now scientists have expanded our understanding of these laws in quantum mechanics.

A conservation law in physics describes the preservation of certain quantities or properties in isolated physical systems over time, such as mass-energy, momentum, and electric charge.

Conservation laws are fundamental to our understanding of the universe because they define the processes that can or cannot occur in nature. For example, the conservation of momentum reveals that within a closed system, the sum of all momenta remains unchanged before and after an event, such as a collision.

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