Kai Sun of the University of Michigan is a humble physics professor with ambitious goals. “I’m mainly a paper-and-pencil type of theorist, doing analytical calculations mostly,” Sun said. “My interests are pretty broad, but basically searching for new fundamental principles and new phenomena, especially new phenomena and new physics previously believed to be impossible.”
In everyday life, all matter exists as either a gas, liquid, or solid. In quantum mechanics, however, it is possible for two distinct states to exist simultaneously. An ultracold quantum system, for instance, can exhibit the properties of both a fluid and a solid at the same time.
The Synthetic Quantum Systems research group at Heidelberg University has now demonstrated this phenomenon using a new experimental approach, by feeding a small amount of energy into a superfluid. They showed that, in a driven quantum system of this kind, sound waves propagate at two different speeds, which points toward coexisting liquid and solid states, a hallmark of supersolidity. The work is published in the journal Nature Physics.
This surprising and seemingly contradictory behavior of two states of matter existing at the same time does not occur at room temperature. But at ultralow temperatures, quantum mechanics takes over, and matter can exhibit fundamentally different properties. When atoms are cooled to such low temperatures, their wave-like nature is dominant. If brought close enough together, many particles merge into one large wave, known as a Bose-Einstein condensate. This state is a superfluid, a fluid that flows without friction.
Quantum researchers have deployed a new algorithm to manage noise in qubits in real time. The method can be applied to a wide range of different qubits, even in large numbers.
Noise is the “ghost in the machine” in the effort to make quantum devices work. Certain quantum devices use qubits—the central component of any quantum processor—and they are extremely sensitive to even small disturbances in their environment.
A collaboration between researchers from the Niels Bohr Institute, MIT, NTNU, and Leiden University has now resulted in a method to effectively manage the noise. The result has been published in PRX Quantum.
The formulation of quantum field theory in Minkowski spacetime, which emerges from the unification of special relativity and quantum mechanics, is based on treating time as a parameter, assuming a fixed arrow of time, and requiring that field operators commute for spacelike separations. This procedure is questioned in the context of quantum field theory in curved spacetime (QFTCS). In 1935, Einstein and Rosen (ER), in their seminal paper [1] proposed that “a particle in the physical Universe has to be described by mathematical bridges connecting two sheets of spacetime” which involved two arrows of time. We further establish that the quantum effects at gravitational horizons aesthetically involve the physics of quantum inverted harmonic oscillators that have phase space horizons. Recently proposed direct-sum quantum theory reconciles the ER’s vision by introducing geometric superselection sectors associated with the regions of spacetime related by discrete transformations. This new understanding of the ER bridges promises a unitary description of QFTCS, along with observer complementarity. Furthermore, we present compelling evidence for our new understanding of ER bridges in the form of large-scale parity asymmetric features in the cosmic microwave background, which is statistically 650 times stronger than the standard scale-invariant power spectrum from the typical understanding of inflationary quantum fluctuations when compared with the posterior probabilities associated with the model given the data. We finally discuss the implications of this new understanding in combining gravity and quantum mechanics.
Gravity and quantum mechanics.
While superconducting qubits are great at fast calculations, they struggle to store information for long periods. A team at Caltech has now developed a clever solution: converting quantum information into sound waves. By using a tiny device that acts like a miniature tuning fork, the researchers were able to extend quantum memory lifetimes up to 30 times longer than before. This breakthrough could pave the way toward practical, scalable quantum computers that can both compute and remember.
A group of theoretical physicists has shown that quantum entanglement obeys universal principles in every dimension by applying thermal effective theory. Their findings were recently published in the journal Physical Review Letters, where the paper was selected as an Editors’ Suggestion.
“This study is the first example of applying thermal effective theory to quantum information. The results of this study demonstrate the usefulness of this approach, and we hope to further develop this approach to gain a deeper understanding of quantum entanglement structures,” said lead author and Kyushu University Institute for Advanced Study Associate Professor Yuya Kusuki.
The same technology behind MRI images of injury or disease also powers nuclear magnetic resonance (NMR) spectroscopy, which is used to analyze biological molecules for research on diseases and therapeutics. While NMR spectroscopy produces valuable data about the structure of molecules, the resolution is too low to sense individual atoms.
Now, quantum researchers at Purdue University are advancing an approach that could improve the resolution of NMR spectroscopy to the atomic scale and may also have applications in developing quantum computing and quantum communications.
“Conventional NMR spectroscopy is limited to measuring large samples of molecules. We’re interested in developing technologies that can detect and analyze a single molecule,” said Tongcang Li, professor of physics and astronomy in the College of Science and of electrical and computer engineering in the College of Engineering.
Quantum technologies, devices that work by leveraging quantum mechanical effects, could outperform classical technologies in some fields and settings. The so-called spin (i.e., intrinsic angular momentum) carried by quantum particles is central to the functioning of quantum systems, as it can store quantum information.
To reliably share quantum information across a network, however, spins need to be linked to photons (i.e., particles of light). For decades, engineers and quantum physicists have thus been trying to devise approaches to interface spins and photons.
One strategy to achieve this entails the use of quantum dots, nanoscale semiconductor structures that can trap electrons or holes in distinct energy levels. When placed in carefully engineered optical resonators known as microcavities, these structures can generate individual photons. Nonetheless, ensuring that the coherence of spins is not disrupted by magnetic noise originating from nearby nuclear spins and thus facilitating the preservation of quantum information over time has so far proved challenging.