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Category: quantum physics – Page 705

Quantum Annealing Pioneer D-Wave Introduces Expanded Hybrid Solver

D-Wave Systems, a pioneer in quantum annealing-based computing, today announced significant upgrades to its constrained quadratic model (CQM) hybrid solver that should make it easier to use and able to tackle much larger problems, said the company. The model can now handle optimization problems with up to 1 million variables (including continuous variables) and 100,000 constraints. In addition, D-Wave has introduced a “new [pre-solver] set of fast classical algorithms that reduces the size of the problem and allows for larger models to be submitted to the hybrid solver.”

While talk of using hybrid quantum-classical solutions has intensified recently among the gate-based quantum computer developer community, D-Wave has actively explored hybrid approaches for use with its quantum annealing computers for some time. It introduced a hybrid solver service (HSS) as part its Leap web access portal and Ocean SDK development kit that D-Wave in 2020. The broad hybrid idea is to use classical compute resources where they make sense – for example, GPUs perform matrix multiplication faster – and use quantum resources where they add benefit.

The HHS also relies on familiar tools and helps deal with the nagging challenge of squeezing large practical problems onto, relatively speaking, D-Wave’s small quantum systems. Its systems are massive (Advantage has 2,000 qubits, Advantage2 is expected to have 5,000 qubits) compared with current gate-based quantum computer sizes (IBM is expected to soon debut a 400-plus qubit processor). But quantum annealing is a different beast and works differently. In most ways, the comparison is not at all apples-to-apples.

Toward large-scale fault-tolerant universal photonic quantum computing

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Photonic quantum computing is one of the leading approaches to universal quantum computation. However, large-scale implementation of photonic quantum computing has been hindered by its intrinsic difficulties, such as probabilistic entangling gates for photonic qubits and lack of scalable ways to build photonic circuits. Here, we discuss how to overcome these limitations by taking advantage of two key ideas which have recently emerged. One is a hybrid qubit-continuous variable approach for realizing a deterministic universal gate set for photonic qubits. The other is the time-domain multiplexing technique to perform arbitrarily large-scale quantum computing without changing the configuration of photonic circuits. These ideas together will enable scalable implementation of universal photonic quantum computers in which hardware-efficient error correcting codes can be incorporated. Furthermore, all-optical implementation of such systems can increase the operational bandwidth beyond terahertz in principle, ultimately enabling large-scale fault-tolerant universal quantum computers with ultrahigh operation frequency.

New Measurements Provide a Glimpse of the Quantum Future

A multi-institutional team has created an efficient method for measuring high-dimensional qudits encoded in quantum frequency combs, a kind of photon source, on a single optical chip using already available experimental and computational resources.

Despite the fact that the word “qudit” may appear to be a typo, this less well-known relative of the qubit, or quantum bit, has the ability to carry more data and is more noise-resistant, two crucial characteristics required to enhance the performance of quantum networks, quantum key distribution systems, and eventually the quantum internet.

In contrast to traditional computer bits, which classify data as ones or zeros, qubits can hold values of one, zero, or both. This is due to superposition, a phenomenon that enables several quantum states to exist simultaneously. Qudit’s “d” refers to the variety of levels or values that may be encoded on a photon. Traditional qubits only have two levels, but by adding more levels, they become qudits.

A scalable quantum memory with a lifetime over 2 seconds and integrated error detection

Quantum memory devices can store data as quantum states instead of binary states, as classical computer memories do. While some existing quantum memory technologies have achieved highly promising results, several challenges will need to be overcome before they can be implemented on a large scale.

Researchers at the AWS Center for Quantum Networking and Harvard University have recently developed a promising capable of error detection and with a lifetime or coherence time (i.e., the time for which a quantum memory can hold a superposition without collapsing) exceeding 2 seconds. This memory, presented in a paper in Science, could pave the way towards the creation of scalable quantum networks.

Quantum networks are systems that can distribute entangled , or qubits, to users who are in different geographic locations. While passing through the networks, qubits are typically encoded as photons (i.e., single particles of light).

Creating quantum-entangled networks of atomic clocks and accelerometers

Researchers affiliated with the Q-NEXT quantum research center show how to create quantum-entangled networks of atomic clocks and accelerometers—and they demonstrate the setup’s superior, high-precision performance.

For the first time, scientists have entangled atoms for use as networked , specifically, atomic clocks and accelerometers.

The research team’s experimental setup yielded ultraprecise measurements of time and acceleration. Compared to a similar setup that does not draw on , their time measurements were 3.5 times more precise, and acceleration measurements exhibited 1.2 times greater precision.

Scientists Invent ‘Quantum Watch’, a Mind-Bending New Way to Measure Time

“To our knowledge, the concept of obtaining time fingerprints, and therefore avoiding the need to measure time zero, is completely novel,” Berholts said in an email. She added that the new invention is a watch, not a clock, because “a clock requires keeping track of time” whereas “a watch simply provides the time.”

“The quantum watch provides a fingerprint representing a specific time, and hence only requires interaction when initiating and reading out the time,” she explained. “All other devices require keeping track of time. This differentiation comes from the fact that the quantum watch, unlike all the other clocks, measures times in a different way.”

Chiral orbit currents create new quantum state

Physicists have discovered a new quantum state in a material with the chemical formula Mn3SiTe6. The new state forms due to long-theorized but never previously observed internal currents that flow in loops around the material’s honeycomb-like structure. According to its discoverers, this new state could have applications for quantum sensors and memory storage devices for quantum computers.

Mn3SiTe6 is a ferrimagnet, meaning that its component atoms have opposing but unequal magnetic moments. It usually behaves like an insulator, but when physicists led by Gang Cao of the University of Colorado, Boulder, US, exposed it to a magnetic field applied along a certain direction, they found that it became dramatically more conducting – almost like it had morphed from being a rubber to a metal.

This effect, known as colossal magnetoresistance (CMR), is not itself new. Indeed, physicists have known about it since the 1950s, and it is now employed in computer disk drives and many other electronic devices, where it helps electric currents shuttle across along distinct trajectories in a controlled way.

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