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Category: quantum physics – Page 196

Scientists develop novel high-fidelity quantum computing gate

Researchers from the RIKEN Center for Quantum Computing and Toshiba have succeeded in building a quantum computer gate based on a double-transmon coupler (DTC), which had been proposed theoretically by Hayato Goto, Senior Fellow at Toshiba, as a device that could significantly enhance the fidelity of quantum gates. Using this, they achieved a fidelity of 99.90 percent for a two-qubit device known as a CZ gate and 99.98 percent for a single-qubit gate. This breakthrough, which was carried out as part of the Q-LEAP project, not only boosts the performance of existing noisy intermediate-scale quantum (NISQ) devices but also helps pave the way for the realization of fault-tolerant quantum computation through effective quantum error correction.

The DTC is a new kind of tunable coupler composed of two fixed-frequency transmons—a type of qubit that is relatively insensitive to charge noise—coupled through a loop with an additional Josephson junction. Its architecture addresses one of the most pressing challenges in quantum computing: the development of hardware to entangle qubits in a high-fidelity manner. High gate fidelity is essential for minimizing errors and enhancing the reliability of quantum computations. The DTC scheme stands out by achieving both suppressed residual interaction and rapid high-fidelity two-qubit gate operations, even for highly detuned qubits. Though fidelity of 99.9 percent has been routinely achieved for single-qubit gates, error rates for two-qubit gates are typically 0.5 percent or more, mainly due to interactions between the qubits known as the ZZ interaction.

The key to the current work, published in Physical Review X, is the construction of qubits using state-of-the-art fabrication techniques and gate optimization using a type of machine learning known as reinforcement learning. These approaches allowed the researchers to translate the theoretical potential of the DTC into practical application. They used these approaches to balance two types of remaining errors—leakage error and decoherence error—that remained within the system, selecting a length of 48 nanoseconds as an optimal compromise between the two error sources. Thanks to this, they achieved fidelity levels among the highest reported in the field.

Twisted light gives electrons a spinning kick: Researchers develop a novel way to control quantum interactions

It’s hard to tell when you’re catching some rays at the beach, but light packs a punch. Not only does a beam of light carry energy, it can also carry momentum. This includes linear momentum, which is what makes a speeding train hard to stop, and orbital angular momentum, which is what the Earth carries as it revolves around the sun.

In a new paper, scientists seeking better methods for controlling the quantum interactions between light and matter have demonstrated a novel way to use light to give electrons a spinning kick. They reported the results of their experiment, which shows that a light beam can reliably transfer to itinerant electrons in graphene, on Nov. 26, 2024, in the journal Nature Photonics.

Having tight control over the way that light and matter interact is an essential requirement for applications like quantum computing or quantum sensing. In particular, scientists have been interested in coaxing electrons to respond to some of the more exotic shapes that light beams can assume.

Simple method can recover and recycle quantum dots in microscopic lasers

Researchers have discovered a way to recycle the tiny particles used to create supraparticle lasers, a technology that precisely controls light at a very small scale. The breakthrough could help manage these valuable materials in a more sustainable way.

Supraparticle lasers work by trapping light inside a tiny sphere made of special particles called quantum dots, which can absorb, emit, and amplify light very efficiently.

They are made by mixing quantum dots in a solution that helps them stick together in tiny bubbles. However, not all attempts succeed, and even successful lasers degrade over time. This leads to wasted materials, which can be expensive.

Cooling with light: Exploring optical cooling in semiconductor quantum dots

Cooling systems are an integral part of many modern technologies, as heat tends to wear down materials and decrease performance in several ways. In many cases, however, cooling can be an inconvenient and energy-intensive process. Accordingly, scientists have been seeking innovative and efficient methods to cool substances down.

Solid-state optical cooling is a prominent example that leverages a very unique phenomenon called anti-Stokes (AS) emission. Usually, when materials absorb photons from incoming light, their electrons transition into an “excited” state.

Under ideal conditions, as electrons return to their original state, part of this excess energy is released as light, while the rest is converted into heat.

Synthetic Dimension Breakthrough Propels Quantum Tech to New Heights

Researchers at INRS have developed a synthetic photonic lattice capable of generating and manipulating quantum states of light, paving the way for promising advancements in applications ranging from quantum computing to secure quantum communication protocols.

A study co-directed by Professor Roberto Morandotti of Institut national de la recherche scientifique (INRS) in collaboration with teams from Germany, Italy, and Japan paves the way for innovative solutions that could enable the development of a system to process quantum information with both simplicity and power.

Their work, just published in the journal Nature Photonics, presents a method for manipulating the photonic states of light in a never-before-seen way, offering greater control over the evolution of photon propagation. This control makes it possible to improve the detection and number of photon coincidences, as well as the efficiency of the system.

1st-of-its-kind Cryogenic Transistor is 1,000 Times More Efficient And Could Lead to Much More Powerful Quantum Computers

Conventional components perform incredibly inefficiently at these sub-freezing temperatures, the scientists said. They’re also very hard to maintain — as more and more qubits are added to a system, the more heat is emitted, which makes it more difficult and expensive to sustain these ultralow temperatures.

Because the new transistor — dubbed the “cryo-CMOS transistor” — is optimized to operate at temperatures under 1 K and emit near-zero heat, it offers plenty of advantages over traditional electronics, representatives of the Finnish company SemiQon, which developed the transistor, said in a statement.

An unconditional distribution learning advantage with shallow quantum circuits

https://scirate.com/arxiv/2411.

Researchers present a #quantummachinelearning advantage of families of constant depth local quantum circuits over reasonably constrained log-log-depth classical circuits.

Quantum…

One of the core challenges of research in quantum computing is concerned with the question whether quantum advantages can be found for near-term quantum circuits that have implications for practical applications. Motivated by this mindset, in this work, we prove an unconditional quantum advantage in the probably approximately correct (PAC) distribution learning framework with shallow quantum circuit hypotheses. We identify a meaningful generative distribution learning problem where constant-depth quantum circuits using one and two qubit gates (QNC^0) are superior compared to constant-depth bounded fan-in classical circuits (NC^0) as a choice for hypothesis classes. We hence prove a PAC distribution learning separation for shallow quantum circuits over shallow classical circuits. We do so by building on recent results by Bene Watts and Parham on unconditional quantum advantages for sampling tasks with shallow circuits, which we technically uplift to a hyperplane learning problem, identifying non-local correlations as the origin of the quantum advantage.

Submitted 23 Nov 2024 to Quantum Physics [quant-ph]

Subjects: quant-ph cs.AI.

Can Quantum Computers Solve the Many-Body Puzzle? Physicists Develop New Metric

The V-score benchmarks classical and quantum algorithms in solving the many-body problem. The study highlights quantum computings potential for tackling complex material systems while providing an open-access framework for future research innovations.

Scientists aspire to use quantum computing to explore complex phenomena that have been difficult for current computers to analyze, such as the characteristics of novel and exotic materials. However, despite the excitement surrounding each announcement of “quantum supremacy,” it remains challenging to pinpoint when quantum computers and algorithms will offer a clear, practical advantage over classical systems.

A large collaboration led by Giuseppe Carleo, a physicist at the Swiss Federal Institute for Technology (EPFL) in Lausane and the member of the National Center for Competence in Research NCCR MARVEL, has now introduced a method to compare the performance of different algorithms, both classical and quantum ones, when simulating complex phenomena in condensed matter physics. The new benchmark, called V-score, is described in an article just published in Science.

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