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In leap for quantum computing, silicon quantum bits establish a long-distance relationship – Quantaneo, the Quantum Computing Source

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Credit: Felix Borjans, Princeton University

Imagine a world where people could only talk to their next-door neighbor, and messages must be passed house to house to reach far destinations.

Until now, this has been the situation for the bits of hardware that make up a silicon quantum computer, a type of quantum computer with the potential to be cheaper and more versatile than today’s versions.

Now a team based at Princeton University has overcome this limitation and demonstrated that two quantum-computing components, known as silicon “spin” qubits, can interact even when spaced relatively far apart on a computer chip. The study was published in the journal Nature.

“The ability to transmit messages across this distance on a silicon chip unlocks new capabilities for our quantum hardware,” said Jason Petta, the Eugene Higgins Professor of Physics at Princeton and leader of the study. “The eventual goal is to have multiple quantum bits arranged in a two-dimensional grid that can perform even more complex calculations. The study should help in the long term to improve communication of qubits on a chip as well as from one chip to another.”

Quantum computers have the potential to tackle challenges beyond the capabilities of everyday computers, such as factoring large numbers. A quantum bit, or qubit, can process far more information than an everyday computer bit because, whereas each classical computer bit can have a value of 0 or 1, a quantum bit can represent a range of values between 0 and 1 simultaneously.

To realize quantum computing’s promise, these futuristic computers will require tens of thousands of qubits that can communicate with each other. Today’s prototype quantum computers from Google, IBM and other companies contain tens of qubits made from a technology involving superconducting circuits, but many technologists view silicon-based qubits as more promising in the long run.

Silicon spin qubits have several advantages over superconducting qubits. The silicon spin qubits retain their quantum state longer than competing qubit technologies. The widespread use of silicon for everyday computers means that silicon-based qubits could be manufactured at low cost.

The challenge stems in part from the fact that silicon spin qubits are made from single electrons and are extremely small.
 
“The wiring or ‘interconnects’ between multiple qubits is the biggest challenge towards a large scale quantum computer,” said James Clarke, director of quantum hardware at Intel, whose team is building silicon qubits using using Intel’s advanced manufacturing line, and who was not involved in the study. “Jason Petta’s team has done great work toward proving that spin qubits can be coupled at long distances.”

To accomplish this, the Princeton team connected the qubits via a “wire” that carries light in a manner analogous to the fiber optic wires that deliver internet signals to homes. In this case, however, the wire is actually a narrow cavity containing a single particle of light, or photon, that picks up the message from one qubit and transmits it to the next qubit.

The two qubits were located about half a centimeter, or about the length of a grain of rice, apart. To put that in perspective, if each qubit were the size of a house, the qubit would be able to send a message to another qubit located 750 miles away.

The key step forward was finding a way to get the qubits and the photon to speak the same language by tuning all three to vibrate at the same frequency. The team succeeded in tuning both qubits independently of each other while still coupling them to the photon. Previously the device’s architecture permitted coupling of only one qubit to the photon at a time.

“You have to balance the qubit energies on both sides of the chip with the photon energy to make all three elements talk to each other,” said Felix Borjans, a graduate student and first author on the study. “This was the really challenging part of the work.”

Each qubit is composed of a single electron trapped in a tiny chamber called a double quantum dot. Electrons possess a property known as spin, which can point up or down in a manner analogous to a compass needle that points north or south. By zapping the electron with a microwave field, the researchers can flip the spin up or down to assign the qubit a quantum state of 1 or 0.

“This is the first demonstration of entangling electron spins in silicon separated by distances much larger than the devices housing those spins,” said Thaddeus Ladd, senior scientist at HRL Laboratories and a collaborator on the project. “Not too long ago, there was doubt as to whether this was possible, due to the conflicting requirements of coupling spins to microwaves and avoiding the effects of noisy charges moving in silicon-based devices. This is an important proof-of-possibility for silicon qubits because it adds substantial flexibility in how to wire those qubits and how to lay them out geometrically in future silicon-based ‘quantum microchips.'”

The communication between two distant silicon-based qubits devices builds on previous work by the Petta research team. In a 2010 paper in the journal Science, the team showed it is possible to trap single electrons in quantum wells. In the journal Nature in 2012, the team reported the transfer of quantum information from electron spins in nanowires to microwave-frequency photons, and in 2016 in Science they demonstrated the ability to transmit information from a silicon-based charge qubit to a photon. They demonstrated nearest-neighbor trading of information in qubits in 2017 in Science. And the team showed in 2018 in Nature that a silicon spin qubit could exchange information with a photon.

Jelena Vuckovic, professor of electrical engineering and the Jensen Huang Professor in Global Leadership at Stanford University, who was not involved in the study, commented: “Demonstration of long-range interactions between qubits is crucial for further development of quantum technologies such as modular quantum computers and quantum networks. This exciting result from Jason Petta’s team is an important milestone towards this goal, as it demonstrates non-local interaction between two electron spins separated by more than 4 millimeters, mediated by a microwave photon. Moreover, to build this quantum circuit, the team employed silicon and germanium—materials heavily used in the semiconductor industry.”

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Starship SN8 prepares for test series – First sighting of Super Heavy – NASASpaceflight.com

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Starship SN8 prepares for test series – First sighting of Super Heavy – NASASpaceFlight.com

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Chang'e-4 lander finds radiation levels on the moon 2.6 times higher than at space station – Firstpost

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As the US prepares to return humans to the Moon this decade, one of the biggest dangers future astronauts will face is space radiation that can cause lasting health effects, from cataracts to cancer and neurodegenerative diseases.

Though the Apollo missions of the 1960s and 1970s proved it was safe for people to spend a few days on the lunar surface, NASA did not take daily radiation measurements that would help scientists quantify just how long crews could stay.

This question was resolved Friday after a Chinese-German team published in the journal Science Advances the results of an experiment carried out by China’s Chang’E 4 lander in 2019.

“The radiation of the Moon is between two and three times higher than what you have on the ISS (International Space Station),” co-author Robert Wimmer-Schweingruber, an astrophysicist at the University of Kiel told AFP.

“So that limits your stay to approximately two months on the surface of the Moon,” he added, once the radiation exposure from the roughly week-long journey there, and week back, is taken into account.

There are several sources of radiation exposure: galactic cosmic rays, sporadic solar particle events (for example from solar flares), and neutrons and gamma rays from interactions between space radiation and the lunar soil.

Scientist-astronaut Harrison Schmitt collecting lunar rake samples during the first Apollo 17. Schmitt was the lunar module pilot for the mission. The Lunar Rake is used to collect discrete samples of rocks and rock chips of different sizes. Image courtesy: NASA

Radiation is measured using the unit sievert, which quantifies the amount absorbed by human tissues.

The team found that the radiation exposure on the Moon is 1,369 microsieverts per day – about 2.6 times higher than the International Space Station crew’s daily dose.

The reason for this is that the ISS is still partly shielded by the Earth’s protective magnetic bubble, called the magnetosphere, which deflects most radiation from space.

Earth’s atmosphere provides additional protection for humans on the surface, but we are more exposed the higher up we go.

“The radiation levels we measured on the Moon are about 200 times higher than on the surface of the Earth and five to 10 times higher than on a flight from New York to Frankfurt,” added Wimmer-Schweingruber.

NASA is planning to bring humans to the Moon by 2024 under the Artemis mission and has said it has plans for a long term presence that would include astronauts working and living on the surface.

For Wimmer-Schweingruber there is one work-around if we want humans to spend more than two or three months: build habitats that are shielded from radiation by coating them with 80 centimeters (30 inches) of lunar soil.

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NASA’s New Budget for Artemis? $28 Billion – Universe Today

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It’s no exaggeration to say that NASA’s plans to return astronauts to the Moon has faced its share of challenges. From its inception, Project Artemis has set some ambitious goals, up to and including placing “the first woman and next man” on the Moon by 2024. Aside from all the technical challenges that this entails, there’s also the question of budgets. As the Apollo Era taught us, reaching the moon in a few years doesn’t come cheap!

Funding is an especially sticky issue right now because of the fact that we’re in an election year and NASA may be dealing with a new administration come Jan of 2021. In response, NASA announced a budget last week (Mon. Sept 21st) that put a price tag on returning astronauts to the Moon. According to NASA, it will cost taxpayers $28 billion between 2021 and 2025 to make sure Project Artemis’ meets its deadline of 2024.

On the same day during a phone briefing with journalists, NASA Administrator Jim Bridenstine noted that “political risks” are often the biggest obstacle to NASA’s work. This is perhaps a reference to the fact that NASA’s plans and goals have forcible shifted over the past decade or so in response to the changing priorities of new administrations.

Artist’s illustration of the new spacesuit NASA is designing for Artemis astronauts. It’s called the xEMU,, or Exploration Extravehicular Mobility Unit. Image Credit: NASA

When he took office in 2009, President Obama and his cabinet inherited the Constellation Program initiated by the Bush administration in 2005. This program aimed to create a new generation of launch systems and spacecraft to return astronauts to the Moon by 2020 at the latest. However, due to the then-current economic crisis and recommendations that the 2020 deadline could not be reached, it was canceled.

A year later, the Obama administration initiated NASA’s “Journey to Mars,” which picked up much of Constellation’s architecture but shifted the focus to a crewed mission to Mars by the 2030s. By 2017, VP Pence announced that the Trump administration’s focus would be on returning to the Moon within the 2020s. By March of 2019, Project Artemis was officially unveiled and NASA was charged with returning to the Moon in five years.

Approval for this funding now falls to Congress, which will be looking at elections by November 3rd. This year, in addition to deciding who will be president, 434 of the 435 Congressional districts across all 50 US states and 33 class 2 Senate seats will be contested. Come January, NASA could be dealing with an entirely new government.

According to Bridenstine, the first tranche of funding ($3.2 billion) must be approved by Christmas in order for NASA to remain “on track for a 2024 moon landing.” In total, NASA will require a full $16 billion in order to fund the development of the human landing system (HLS) – aka. a lunar lander – that will allow the crew of the Artemis III mission (one man and one woman) to land on the surface of the Moon.

The three top HLS concepts for NASA’s Project Artemis. Credit: NASA

At present, three major companies are competing to see which of their concepts NASA will choose. They include SpaceX, which presented NASA with a modified version of their Starship designed, altered to accommodate lunar landings. Then there’s Alabama-based Dynetics’ Human Landing System (DHLS), a vehicle that will provide both descent and ascent capabilities.

Rounding out the competitors is Blue Origin, meanwhile is collaborating on a design for an Integrated Lander Vehicle (ILV) that will consist of three elements – the descent, transfer, and ascent elements – designed by Blue Origin, Northrop Grumman, and Lockheed Martin, respectively. The winning design will either be integrated with the Orion capsule carrying the crew to the Moon or will launch on its own atop a company rocket.

Bridenstine also took the opportunity to set the record straight regarding where the Artemis III mission would be landing. This was in response to a previous statement he made during an online meeting of the Lunar Exploration Analysis Group (LEAG), which seemed to hint that the Artemis crews might revisit the Apollo sites.

“If you’re going to go to the equatorial region again, how are you going to learn the most?” he said. “You could argue that you’ll learn the most by going to the places where we put gear in the past. There could be scientific discoveries there and, of course, just the inspiration of going back to an original Apollo site would be pretty amazing as well.”

Artist’s impression of surface operations on the Moon. Credit: NASA

During Monday’s phone briefing, however, Bridenstine emphasized that the mission will be heading to the South Pole-Aitken Basin:

“To be clear, we’re going to the South Pole. There’s no discussion of anything other than that. The science that we would be doing is really very different than anything we’ve done before. We have to remember during the Apollo era, we thought the moon was bone dry. Now we know that there’s lots of water ice and we know that it’s at the South Pole.”

Investigations of this ice and other resources will be intrinsic to long-term plans to create the Artemis Base Camp. The current schedule has the Artemis I flight (which will be uncrewed) taking place by November of 2021. This will be the inaugural flight of NASA’s Space Launch System (SLS) flying with the Orion space capsule. Artemis II is scheduled for 2023, and will take a crew of astronauts around the Moon but will not attempt a lunar landing.

In 2024, the long-awaited Artemis III mission will occur and will see astronauts land on the surface for a week of operations and up to five operations on the surface. Beyond 2024, NASA plans to deploy the various segments that make up the Lunar Gateway, which will facilitate more long-term missions to the lunar surface and allow for the construction of the Artemis Base Camp.

Further Reading: Phys.org

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