March 18, 2019
Want to travel back in time? Russian physicists have indeed turned back time with the use of a quantum computer. Let's put one of those in a DeLorean and see what happens.
Learn about this and more interesting stories from the scientific community in today's issue.
P.S. Did you miss an issue? You can read every issue from the Gophercentral library of newsletters on our exhaustive archives page. Thousands of issues, all of your favorite publications in chronological order. You can read AND comment. Just click
*-- Scientists turn back time with quantum computer --*
 Physicists in Russia have turned back time using a quantum computer.
For some time, researchers at the Moscow Institute of Physics and Technology have been working to prove the second law of thermodynamics can be violated.
"That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future," lead researcher Gordey Lesovik said in a news release.
Lesovik and his colleagues have already published two papers on the subject. For the latest study, scientists teamed with physicists in the United States and Switzerland to construct a quantum computer capable of violating the second law.
"We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time," Lesovik said.
The second law of thermodynamics posits that an isolated system can only remain static or evolve toward a state of chaos. If a video of a cue ball colliding with a pyramid of billiard balls was played backward and forward, the viewer would quickly be able to discern which direction revealed the actual sequence of events. The viewer intuitively understands the second law of thermodynamics.
There are no physical laws that explicitly prevent the violation of the second law, but violations have remained unobserved.
To better understand the odds of the second law being violated, quantum physicists analyzed the behavior individual particles.
"Suppose the electron is localized when we begin observing it," said Andrey Lebedev, who works at both MIPT and ETH Zurich. "This means that we're pretty sure about its position in space. The laws of quantum mechanics prevent us from knowing it with absolute precision, but we can outline a small region where the electron is localized."
Schrödinger's equation describes the evolution of a particle's electron state. The region of space containing the electron quickly expands. Chaos increases as systems scale.
"However, Schrödinger's equation is reversible," said Valerii Vinokur, a researcher at the Argonne National Laboratory in the United States. "Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a 'smeared' electron localizing back into a small region of space over the same time period."
Researchers crunched the numbers and found that if 10 billion freshly localized electrons were observed every second for the entirety of the universe's lifetime, 13.7 billion years, only one particle would be observed reversing time -- spontaneously localizing against the arrow of time.
Next, scientists attempted to manufacture a violation of the second law of thermodynamics. They built a quantum computer with two and three superconducting qubits. Physicists used the quantum computer to conduct a four-stage experiment.
Stage one features an ordered state, with each qubit grounded at zero, like a single electron confined to a small localized region. During the second stage, order is lost. Scientists used an evolution program on the quantum computer to trigger the degradation of order, causing the qubits to begin assuming an increasingly complex pattern of zeros and ones, like an electron getting smeared out across a larger and larger region of space.
For stage three, scientists used another program to reverse time, causing the qubits to evolve from chaos to order -- to reground themselves at zero. For stage four, the evolution program is relaunched from the second stage, causing the qubits to reverse time and revert to their earlier state.
When scientists used a two-qubit computer to conduct the four stage experiment, they observed qubits moving from chaos to order every time. When they introduced a third qubit, the computer produced more errors, and the qubits were able to reverse time only half of the time.
Researchers suggest their findings -- published this week in the journal Scientific Reports -- could be used to improve the precision of quantum devices.
"Our algorithm could be updated and used to test programs written for quantum computers and eliminate noise and errors," Lebedev said.
*-- Hydroelectric dams harm coastal ecosystems downstream --*
According to a new study, coastal ecosystems suffer when hydroelectric dams are built upstream.
Mangrove forests, wetlands and other estuarine habitats are already facing the threat of rising sea levels. Now, new research suggests these ecosystems are disrupted by upstream dam construction.
For the new study -- published in the journal Science Advances -- scientists studied four rivers in the Mexican Pacific states of Sinaloa and Nayarit, two dammed and two mostly unobstructed.
The Santiago and Fuerte rivers both feature large hydroelectric dams that produce large amounts of electricity. The two dams block 95 percent of the flow in each river. San Pedro and Acaponeta remain 75 percent unobstructed, making them relatively free-flowing. All four rivers follow parallel paths from the mountains to the Pacific and run through similar terrain.
As the new research revealed, more than a million tons of sediment are blocked by the two hydroelectric dams. Sediment and fresh water are the life blood of coastal ecosystems. Since the Santiago and Fuerte became obstructed by dams, the rivers' annual rate of coastal land loss has increased 21 hectares.
Coastal lands in the mouths of the San Pedro and Acaponeta remained stable during the same time period.
"Similar processes of damming rivers and controlling water flows are destroying estuaries and coasts in many parts of the world," lead study author Exequiel Ezcurra, a professor at the University of California, Riverside, said in a news release. "Despite the huge implications for ecosystem conservation, the process of coastal degradation as a result of large dams has not been well-studied or quantified using a strict comparative approach."
Wetlands provide a range of important ecological and economic benefits. In addition to providing protections against flooding and storm surges, estuarine habitats support commercial fish stocks. Estuarine habitats also shelter a large variety of unique plant and animal species, as well as help sequester carbon.
For the latest study, scientists estimated the economic value of the services lost when a river is dammed at $10 million annually.
"The benefits of ephemeral jobs generated around the construction of the dam need to be weighed against the long-term costs the dam will cause to local livelihoods," said co-author Octavio Aburto-Oropeza, professor Scripps Institution of Oceanography.
|