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Quantum sensing can outperform classical sensing by placing the sensor in an initial state that optimally measures the target. However, choosing this optimal state requires having some preknowledge, such as knowing the orientation of a magnetic field in order to measure its strength. A new experiment overcomes this limitation using two entangled quantum bits (qubits), which are manipulated in a way that is equivalent to a qubit traveling back in time [1]. Through this “time travel,” the qubits can be placed in an optimal state without any preknowledge.

“Our work addresses a specific kind of problem that plagues many sensing setups: you have to know which direction to point the sensor,” explains Kater Murch from Washington University in St. Louis. When measuring a magnetic field with a spin qubit, for example, the spin’s rotation will return information about the field strength only if you point it in the optimal direction. Point it in a nonoptimal direction and you’ll get zero information about the field, wasting the measurement.

Murch and his colleagues have devised a protocol in which the probe qubit is entangled with a second qubit, called the ancilla. Following previous work, they show that the entanglement is mathematically equivalent to the ancilla traveling back in time to place the probe in an optimal state [2]. They further show that measuring the ancilla and the probe in a particular sequence can recover information about the field strength in all cases—so no measurement data are wasted as they can be in other protocols. The researchers foresee using this entanglement scheme in situations where a field—or another observable—is changing over time.

A new quantum-system-on-chip enables the efficient control of a large array of qubits, advancing toward practical quantum computing.

Researchers at MIT and MITRE have developed a scalable, modular quantum hardware platform, incorporating thousands of qubits on a single chip, promising enhanced control and scalability. Utilizing diamond color centers, this new architecture supports extensive quantum communication networks and introduces an innovative lock-and-release fabrication process to efficiently integrate these qubits with existing semiconductor technologies.

Quantum Computing Potential

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Researchers at UC Berkeley have enhanced the precision of gravity experiments using an atom interferometer combined with an optical lattice, significantly extending the time atoms can be held in free fall. Despite not yet finding deviations from Newton’s gravity, these advancements could potentially reveal new quantum aspects of gravity and test theories about exotic particles like chameleons or symmetrons.

Twenty-six years ago physicists discovered dark energy — a mysterious force pushing the universe apart at an ever-increasing rate. Ever since, scientists have been searching for a new and exotic particle causing the expansion.

Continue reading “Beyond Gravity: UC Berkeley’s Quantum Leap in Dark Energy Research” »

Stanford’s new tiny, cheap laser:

Researchers have achieved a potentially groundbreaking innovation in laser technology by developing a titanium-sapphire (Ti: sapphire) laser on a chip. This new prototype is dramatically smaller, more efficient, and less expensive than its predecessors, marking a significant leap forward with a technology that has broad applications in industry, medicine, and beyond.

Ti: sapphire lasers are known for their unmatched performance in quantum optics, spectroscopy, and neuroscience due to their wide gain bandwidth and ultrafast light pulses. However, their bulky size and high cost have limited their widespread adoption. Traditional Ti: sapphire lasers occupy cubic feet in volume and can cost hundreds of thousands of dollars, in addition to requiring high-powered lasers costing $30,000 each to feed it the energy it needs to operate.

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For the last seven decades, astrophysicists have theorized the existence of “kugelblitze,” black holes caused by extremely high concentrations of light.

These special black holes, they speculated, might be linked to astronomical phenomena such as dark matter, and have even been suggested as the power source of hypothetical spaceship engines in the far future.

However, new theoretical physics research by a team of researchers at the University of Waterloo and Universidad Complutense de Madrid demonstrates that kugelblitze are impossible in our current universe. Their research, titled “No black holes from light,” is published on the arXiv preprint server and is forthcoming in Physical Review Letters.

Philosopher Wilfrid Sellars had a term for the world as it appears, the “manifest image.” This is the world as we perceive it. In it, an apple is an apple, something red or green with a certain shape, a range of sizes, a thing that we can eat, or throw.

The manifest image can be contrasted with the scientific image of the world. Where the manifest image has colors, the scientific one has electromagnetic radiation of certain wavelengths. Where the manifest image has solid objects, like apples, the scientific image has mostly empty space, with clusters of elementary particles, held together in configurations due to a small number of fundamental interactions.

The scientific image is often radically different from the manifest image, although how different it is depends on what level of organization is being examined. For many purposes, including scientific ones, the manifest image, which is itself a predictive theory of the world at a certain level or organization, works just fine. For example, an ethologist, someone who studies animal behavior, can generally do so without having to concern themselves about quantum fields and their interactions.

Physicists at TU Graz have determined that certain molecules can be stimulated by pulses of infrared light to generate small magnetic fields. If experimental trials are also successful, this technique could potentially be applied in quantum computer circuits.

When molecules absorb infrared light, they start to vibrate as they receive energy. Andreas Hauser from the Institute of Experimental Physics at Graz University of Technology (TU Graz) used this well-understood process as a basis for exploring whether these vibrations could be harnessed to produce magnetic fields. Since atomic nuclei carry a positive charge, the movement of these charged particles results in the creation of a magnetic field.

Using the example of metal phthalocyanines – ring-shaped, planar dye molecules – Andreas Hauser and his team have now calculated that, due to their high symmetry, these molecules actually generate tiny magnetic fields in the nanometre range when infrared pulses act on them.

While solid-state spin qubits show promise as quantum information platforms, their qubit-to-qubit interactions extend over too short a distance to connect many of them together, posing a problem for complex computations. Now Frankie Fung and colleagues from Harvard University have devised a mechanical method—involving a vibrating nanobeam—to connect distant spin qubits, potentially overcoming this issue [1].

A popular solid-state spin qubit is the nitrogen-vacancy (NV) center, a single-atom defect in a diamond crystal. This system is attractive for quantum information applications, as it has both a light-sensitive electron spin state (which offers a knob for controlling the qubit) and a long-lived nuclear spin state (which acts as memory). But direct interactions between NV centers are limited to a few nanometers.

To lengthen the connections, Fung and his colleagues propose using a nanobeam fitted with a micromagnet as an intermediary between distant NV centers. The idea is then to place a line of NV centers along the length of a scanning-probe-microscope tip and move the tip over the micromagnet. When a particular NV center comes close to the micromagnet, the magnetic-field interaction should entangle the vibrational state of the nanobeam with the spin state of that NV center. This quantum information is then shared with the next NV center along the line.

A physicist investigating black holes has found that, in an expanding universe, Einstein’s equations require that the rate of the universe’s expansion at the event horizon of every black hole must be a constant, the same for all black holes. In turn this means that the only energy at the event horizon is dark energy, the so-called cosmological constant. The study is published on the arXiv preprint server.

“Otherwise,” said Nikodem Popławski, a Distinguished Lecturer at the University of New Haven, “the pressure of matter and curvature of spacetime would have to be infinite at a horizon, but that is unphysical.”

Black holes are a fascinating topic because they are about the simplest things in the universe: their only properties are mass, electric charge and angular momentum (spin). Yet their simplicity gives rise to a fantastical property—they have an event horizon at a critical distance from the black hole, a nonphysical surface around it, spherical in the simplest cases. Anything closer to the black hole, that is, inside the event horizon, can never escape the black hole.