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Category: quantum physics – Page 546

A team of physicists at the Universities of Bristol, Vienna, the Balearic Islands and the Institute for Quantum Optics and Quantum Information (IQOQI-Vienna) has shown how quantum systems can simultaneously evolve along two opposite time arrows—both forward and backward in time.

The study, published in the latest issue of Communications Physics, necessitates a rethink of how the flow of time is understood and represented in contexts where quantum laws play a crucial role.

For centuries, philosophers and physicists have been pondering the existence of time. Yet, in the , our experience seems to extinguish any doubt that time exists and goes on. Indeed, in nature, processes tend to evolve spontaneously from states with less disorder to states with more disorder, and this propensity can be used to identify an arrow of time. In physics, this is described in terms of ‘entropy’, which is the physical quantity defining the amount of disorder in a system.

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Taking a gas enclosed in a vessel as a pictorial example, the aforementioned state can be constructed by entangling the position of the piston with a further auxiliary quantum system, thereby establishing a quantum superposition of the following two processes: (i) a process wherein the gas particles are initially in thermal equilibrium confined in one half of the vessel by a piston, and the piston is pulled outwards, and (ii) the reverse process, in which the piston is pushed towards the gas, starting from an initial state where the gas occupies the entire vessel in thermal equilibrium.

We will now measure the work of the system undergoing the above-mentioned superposition of forward and time-reversal dynamics. In order to implement such a measurement, we formally construct a procedure described by a set of measurement operators forming a completely positive and trace-preserving (CPTP) map. In this regard, we will refer to a standard TPM procedure to measure work in quantum thermodynamic processes13. Implementations of the TPM in quantum setups25,26,27,28,29, as well as suitable extensions30,31,32,33, have recently received increasing attention. Our procedure can be seen as a generalisation of the TPM scheme to situations where different thermodynamic processes are allowed to be superposed, and can consequently interfere.

In the TPM scheme, work is defined as the energy difference between the initial and final states of the system, which are measured through ideal projective measurements of the system Hamiltonian implemented before and after the thermodynamic process associated with the protocol Λ34,35. This measurement scheme can be performed, individually, both for the forward and the time-reversal processes, enabling the construction of the work probability distributions P (W) and \(\tilde{P}(W)\) 0, respectively.

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Sensors introduce an important new method to spot bio-marker for brain diseases Accurate timings of when brain signals fire demonstrated for the first time by the Sussex scientists, which has implications for tracking the onset of brain disease The quantum brain sensors could present a more efficient and accurate alternative to EEG and fMRI scanners.

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A team of researchers from TU Delft managed to design one of the world’s most precise microchip sensors. The device can function at room temperature—a ‘holy grail’ for quantum technologies and sensing. Combining nanotechnology and machine learning inspired by nature’s spiderwebs, they were able to make a nanomechanical sensor vibrate in extreme isolation from everyday noise. This breakthrough, published in the Advanced Materials Rising Stars Issue, has implications for the study of gravity and dark matter as well as the fields of quantum internet, navigation and sensing.

One of the biggest challenges for studying vibrating objects at the smallest scale, like those used in sensors or quantum hardware, is how to keep ambient thermal noise from interacting with their fragile states. Quantum hardware for example is usually kept at near absolute zero (−273.15°C) temperatures, and refrigerators cost half a million euros apiece. Researchers from TU Delft created a web-shaped microchip sensor that resonates extremely well in isolation from room temperature noise. Among other applications, their discovery will make building quantum devices much more affordable.

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Physicists have created a new ultra-thin two-layer material with quantum properties that normally require rare earth compounds. This material, which is relatively easy to make and does not contain rare earth metals, could provide a new platform for quantum computing and advance research into unconventional superconductivity and quantum criticality.

The researchers showed that by starting from seemingly common materials, a radically new quantum state of matter can appear. The discovery emerged from their efforts to create a quantum spin liquid which they could use to investigate emergent quantum phenomena such as gauge theory. This involves fabricating a single layer of atomically thin tantalum disulfide, but the process also creates islands that consist of two layers.

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Friends Lunch with a Member.

Topic: Negative Energy, Quantum Information and Causality.
Speaker: Adam Levine.
Date: November 19, 2021

Einstein’s equations of gravity show that too much negative energy can lead to causality violations and causal paradoxes such as the so-called “grandfather paradox. In quantum mechanics, however, negative energies can arise from intrinsically quantum effects, such as the Casimir effect. Thus, it is not clear that gravity and quantum mechanics can be self-consistently combined. In this talk, Levine will discuss modern advances in understanding the connection between energy and causality in gravity and how quantum gravity avoids obvious paradoxes. He will also explore how this line of thought leads to new insights in quantum field theory, which governs particle physics.

As a physicist, Adam Levine’s research aims to understand the structure of entanglement in quantum field theories and quantum gravity through use of techniques from the study of conformal field theories, as well as quantum information theory and AdS/CFT. With support from the National Science Foundation, Adam is a long term Member in the School of Natural Sciences. He received his Ph.D. from University of California, Berkeley (2019), was a Graduate Fellow at the Kavli Institute for Theoretical Physics (2018), a National Defense Science and Engineering Graduate Fellow (2017−2020), and received the Jeffrey Willick Memorial Award for Outstanding Scholarship in Astrophysics from Stanford University (2015).

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Researchers prepare ‘new type of matter’ to conduct classic wave-particle duality experiment.

The iconic quantum double-slit experiment, which reveals how matter can behave like waves that displays interference and superposition, has for the first time been demonstrated with individual molecules as the slits.

Richard Feynman once said that the double-slit experiment reveals the central puzzles of quantum mechanics, putting us ‘up against the paradoxes and mysteries and peculiarities of nature’.

Richard Zare, Nandini Mukherjee and their co-workers at Stanford University, US, have now shown that when helium atoms collide with deuterium molecules (D2) in quantum superposition of states, the scattering can take two different paths that interfere with one another. The researchers reveal the interference by looking at its effects on the scattered D2 molecules, which lose rotational energy in the collision.

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The ability to precisely control and change properties of a photon, including polarization, position in space, and arrival time, gave rise to a wide range of communication technologies we use today, including the Internet. The next generation of photonic technologies, such as photonic quantum networks and computers, will require even more control over the properties of a photon.

One of the hardest properties to change is a photon’s color, otherwise known as its frequency, because changing the frequency of a photon means changing its energy.

Today, most frequency shifters are either too inefficient, losing a lot of light in the , or they can’t convert light in the gigahertz range, which is where the most important frequencies for communications, computing, and other applications are found.

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