• Kamil Korzekwa and Matteo Lostaglio; publikacja w Physical Review X
For the past three decades, scientists have been harnessing the quantum features of nature to challenge the best-known classical methods of computing, metrology, and cryptography. In all these cases, quantum superposition allows one to perform certain tasks faster, more precisely, or more securely.
For the past three decades, scientists have been harnessing the quantum features of nature to challenge the best-known classical methods of computing, metrology, and cryptography. In all these cases, quantum superposition allows one to perform certain tasks faster, more precisely, or more securely. In a recent paper published in Physical Review X, Kamil Korzekwa and Matteo Lostaglio report a novel quantum advantage that reduces the amount of memory and time needed to implement certain dynamical processes, such as thermodynamic cooling or information processing. In their work, they introduce a unifying framework to theoretically analyze memory and time costs from a mathematical, computational, and thermodynamical point of view, and apply it to study three distinct scenarios where quantum advantages arise. First, they show that there exist stochastic processes that cannot be simulated classically without memory but can be implemented “quantumly” in a memoryless fashion. Second, they prove that for processes that require memory even in the quantum regime, there is an improvement over classical computers in the number of times the memory must be accessed or in its size. Third, they demonstrate that memoryless quantum processes allow for much better control of the system’s state than their classical counterparts. Their findings show that quantum mechanics provides powerful models to simulate stochastic processes and pave the way to the investigation of practical advantages for quantum information processing.
• Patryk Mach, Andrzej Odrzywołek; publikacja w Physical Review Letters
How fast does a moving black hole accrete dark matter?
In a recent paper published in Physical Review Letters Patryk Mach and Andrzej Odrzywołek give the answer to this question. In their work dark matter is modelled as a Vlasov gas of collisionless particles, interacting gravitationally with the black hole. The answer turns out to be quite surprising---the accretion rate (the rate at which the matter falls into the black hole) depends both on the black hole velocity and the temperature of the dark matter. For hot dark matter the accretion rate grows with the black hole speed. The accretion rate of cold dark matter attains a minimum value at some finite black hole velocity. While the accretion of dark matter on black holes is presently rather inefficient (under reasonable assumptions on the black hole mass, its velocity, and the density of the dark matter medium), it could have led to a significant growth of black holes in early cosmological epochs.
• Yi-Fu Cai, Chunshan Lin, Bo Wang, Sheng-Feng Yan; publikacja w Physical Review Letters
The hot big bang expansion of our universe was probably triggered by the cosmic epoch called “reheating” in which a scalar field oscillated about the minimum of potential and decayed into matter and radiation that we observed nowadays.
In a recent paper published in Physical Review Letters Chunshan Lin and his collaborators pointed out that for a large class of modified gravity theories, this cosmic epoch gives rise to a novel sound speed resonance phenomenon on the cosmological stochastic gravitational waves background. The primary signal of this phenomenon is a sharp peak on the stochastic gravitational waves spectrum, which may reach the sensitivity of present and forthcoming gravitational waves experiments. This mechanism provides a promising observational window to test modified gravity. It bridges gravitational wave astronomy with new physics beyond general relativity at high energy scales.