Month: November 2018

Bose Einstein condensates (BECs) have been around for more than 20 years now. One of the best applications of the BEC, it turns out, is as a tool to explore other quantum things, like solids—yes, the properties of solids are determined by quantum mechanics.

Among those solids is a controversial and possibly nonexistent theoretical one: the supersolid. Now, a pair of theoretical physicists has shown that a recently observed BEC “droplet” state may be a way to create a supersolid-like material. That may lead to a way to explore the properties of a supersolid without the difficulties associated with conventional materials.

Bose Einstein condensates

A BEC is a state of matter that requires a specific type of particle. Essentially, the particle world is divided in two: you are either a fermion or a boson. Fermions don’t like each other, so they stack themselves in order of energy, from low to high. Any two fermions that are within touching distance of each other must be different. That might mean different energies, or different spins, or some other property, but they must be different. Pretty much everything is made of fermions, and this stacking is what makes the Universe the way it is.

Bosons are different. Bosons will happily get together and party in the same state. Not only do they not mind having the same state, they love it. If a couple of bosons find themselves in the same state, they will immediately call all their friends and try to get them to join in. And if the bosons have a way to shed enough energy, they will. The result is that it’s relatively easy to create a very cold gas of bosons that are all in exactly the same quantum state, called a BEC.

However, not all bosons and BECs are the same. Although the bosons love to be in the same state, most bosons are composite particles, with some of their components fermions. As a result, there are also forces at work trying to drive atoms out of the BEC. The relative strength between the attraction that pulls the BEC together and the repulsive forces that try to blow it apart is something that is under experimental control.

Exploring weird solids

One of the slightly weirder observations of BECs is that certain types of BEC will form arrays of droplets when the conditions are right. We’ve seen them form a series of evenly spaced globs of relatively high density, but we don’t know why they do this. We also don’t know what properties these droplets have.

In a reasonably thorough exploration of the phenomena, a pair of theoretical physicists have answered some of these questions. First, droplet formation represents a balance of forces. As we said above, the attractive forces pull the BEC together as the repulsive forces push it apart. For the types of BECs that form droplets, the repulsive forces are not just a function of the density but also the atomic number. A small number of atoms can huddle together nice and close. That number cannot grow very large, though, as that would drive atoms away. That means the BEC forms a number of high density droplets that all repel each other. Throw in the confines of the trap that controls the BEC, and a nice regular 2D array of droplets emerge.

The researchers wondered if the droplets are really still part of the same BEC. The thing that makes a BEC a single entity is a kind of collective behavior among its atoms. However, that collective behavior requires that the different BEC droplets be connected. That connection takes the form of atoms moving among them.

The researchers showed that if the trap pressed the droplets close together, atoms are regularly transferred among the different droplets, which would allow the BEC to retain its collective behavior.

But critically, they found that under these conditions, the BEC would resemble something called a supersolid. As the droplets move further apart, atoms can’t move between the droplets anymore. At that point, the BEC doesn’t resemble a supersolid anymore.

The supersolid transition is important because supersolids are still controversial. Supersolids are, well, solid. That is, they retain their shape like conventional solids. But they also do weird things like slide along surfaces without friction, for instance. There have been several experimentalists that claim to have observed the supersolid state, but none have been clear enough to make the claim unequivocal.

Here, we have a tool to explore the supersolid form and its phase transition in detail: a clean environment where the state’s properties can be mapped out thoroughly. That should make it easier to refute or support experimental claims in more traditional solid state physics experiments.

Physical Review Letters, 2018, DOI: 10.1103/PhysRevLett.121.195301. (About DOIs)

Listing image by NIST/JILA/CU-Boulder

Startup

Rivian

created the biggest buzz of the

L.A. Auto Show

by coming out of virtual oblivion to deliver not one but two

battery-electric

off-road vehicles with

supercar

-worthy acceleration and

Tesla

-fighting range figures. So who are these guys and how did they stay so undiscovered all this time?

To be sure, it’s not like the company, which was founded as Mainstream Motors in Florida in 2009 and quickly changed its name to

Avera Automotive

before

settling on Rivian

, flew completely under the radar. But it’s one thing to read about claims of 400-mile-plus driving range, 3-second 0-60 times and 11,000-pound towing capacity, and quite another to see what they’ve actually made — the

R1T pickup truck

and its companion, the

R1S SUV

.

The company was the brainchild of then-26-year-old R.J. Scaringe (he’s now 35), a nature and car enthusiast who grew up on Florida’s Indian River but was frustrated by what he saw as a lack of environmentally sustainable automobiles. Scaringe earned a degree in mechanical engineering from Rochester Polytechnic Institute in New York and later earned a master’s and doctorate from MIT, where he worked on the research team at the Sloan Automotive Laboratory.

Rivian moved to the Detroit area from Florida in 2015 and now makes its de facto headquarters, design and engineering center in a former cash-register factory in suburban

Plymouth

, Mich. “There was literally no sign on the building,” says Ken Shuman, chief communications officer.

RIvian now has four other locations: a battery lab in Irvine, Calif.; a connected car and autonomous research and development center in San Jose, Calif.; a small engineering office in the U.K.; and a manufacturing center under development in Normal, Ill., where the company bought a 2.4-million-square-foot former

Mitsubishi

factory

for a reported $16 million

, with plans to sink more than $40 million into the plant by 2022. Production is set to begin there next year.

“We’ve already got a team of around 60 people in that facility,” says Mark Vinnels, the company’s executive director of engineering and programs. “All the tooling, paint shop, everything. Configuring it for how we’re going to build this car. Those guys are intimately involved with the design of all the components, and have been for a couple of years. So the design for manufacturing, the quality aspirations that we’ve got for the vehicle, that’s a key part of that.”

Just where the company is getting all the money necessary to achieve its dreams remains a closely held secret.

“We’ve got a really strong source of money, financing for the company is solid … good investors who understand motorcars and are in it for the long game, and don’t want to make a quick return and understand that putting cars into production is super difficult and costs a lot of money,” said Vinnels, who joined Rivian 13 months ago after a long stint with

McLaren

and, before that,

Lotus Group

.

“That’s gotta be the foundation of building a solid car company. What you’re seeing here is the result of a lot of work that’s already gone on, on a very sound basis, for what we believe will be a groundbreaking, reliable, safe product when it comes to production. And that’s why we’re not racing to production now. There’s still a lot that we need to do. What you see here reflects production intent … but we recognize that we’ve got to make sure the car’s reliable, the quality’s there.”

Vinnels talks a lot about the on- and off-road capabilities of both models, calling Rivian an “adventure brand.” Its off-road specs are bolstered by quad all-wheel drive independent electric motors, each nearly 200 horsepower, capable of delivering independent, instantaneous torque to each wheel. There’s also unequal-length double-wishbone suspension in front and multi-link suspension in the rear, with dynamic roll control, adaptive dampers and adjustable air suspension, so you can stiffen the ride for extra agility and handling on pavement.

He also dished on the evolution of that unique headlight design, which he said the company “spent a ton of time thinking about.”

“We wanted a face,” he said. “We’re a new brand. Nobody knows who Rivian is. What we want is something that people recognize. Maybe when you leave today, you should pretty much be able to sketch it based on the simplicity and elegance of it. I have to say it’s not something we fell upon easily. We had a lot of hard work, a lot of different designs, even when we were a full-size model of this, we hadn’t focused on that design. In fact it was one of the designers who was working on advanced vehicles, a vehicle we were looking at for 2025, 2026, who sketched this, and we loved it. And we said let’s try it on this model.”

Each model will debut with Level 3 autonomous driving capabilities. Similar to

Tesla

, they’ll get over-the-air software updates. They’ll also have the ability to operate three apps simultaneously, and three screens, including one in the backseat for climate and infotainment.

Order books are now open for a fall 2020 delivery on the R1T pickup and 2021 for the R1S. The former starts at $69,000, or $61,500 after federal

EV

tax credits, while the latter starts at $72,500 ($65,000), Shuman said.

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