We may earn revenue from the products available on this page and participate in affiliate programs. Learn More ›

Whether you bowhunt or just shoot at the range, a good bow case is as important as a good bow sight. Bow cases aren’t just for storage; they’re vital to protect your bow and keep it in operating condition. That means shielding it from the elements, pets, kids, airline baggage handlers, bumpy rides, and pretty much any other hazard you can and can’t think of.

I’ve traveled all over North America with a bow, to hunt and to attend archery tournaments. I’ve also had the opportunity to test almost every bow case on the market in the past ten years. And fortunately, the market is rife with cases designed to house your precious investment. Finding the right one for your needs is an individual task. You know how you live, travel, and how and when you hunt. So you’ll want to find the best bow cases for those conditions and choose the one that best fits your style.

• Best Overall: Easton Bowtruk 4017 Gen 2
• Best Soft Case: Legend Alpha RS
• Best Value Soft Case: Easton Bow-Go 4118 Bow Case
• Best for Air Travel: SKB ATA Double Bow Case
• Best Budget: Plano 110 Protector Series Compact Bow Case
• Best for Crossbows: Tarantula Echo Crossbow Case
• Best Honorable Mention: Pelican 1745 Air
• Mystery Ranch Anchor Point Bow Case
• Sitka Nomad

How I Evaluated the Best Bow Cases

Traveling with a bow to the Midwest, the Arctic circle and everywhere in between, by trucks, airliners, float planes, and boats has taught me what makes a good bow case. I also work at Lancaster Archery Supply, which carries many of the best bow cases available. My experiences with cases guided my selections for the best bow cases that follow.

The Best Bow Cases: Reviews and Recommendations

Best Overall: Easton Bowtruk 4017 Gen 2

See It

Pros

• Best wheels in the industry
• Can use it as a cart to haul other luggage
• Very durable
• Holds a ton of gear besides your bow

Cons

• Expensive
• Requires an external lock to lock it

---

Features

• Dimensions: 40 inches long and 17 inches wide
• Exterior is a waterproof ballistic nylon
• Oversized, sealed-bearing skate wheels
• “Bow burrito” holds bow securely inside the case
• Three pockets for accessories
• Loads of interior room to pack in more gear
• Soft outer material can withstand airline abuse

The original Easton Bowtruk was released in 2020, with a design and features targeting the most demanding bowhunters and target archers. This was meant to be the only bow case they’d ever need, whether they were traveling to the home archery range or to a distant destination only accessible by air.

With three years of user data under their belts, Easton’s engineers tweaked the Bowtruk in 2023 to produce the Bowtruk Gen 2. As good as the original case was, this one’s even better.

It’s built from a waterproof ballistic nylon, similar to what’s used in bulletproof vests. That makes the Bowtruk virtually indestructible – even when tossed around by airline baggage handlers. But the flexible exterior material also makes the Bowtruk feel less cumbersome than hard cases if you’re simply traveling from home to the local range.

Inside the case, there’s a fleece wrap with straps that holds your bow in place like a burrito. Damage occurs in bow cases when the bow is able to move around.

With lots of extra room, plan on stashing plenty of clothes on top of the bow burrito to take full advantage of that 50-pound weight limit most airlines have on luggage before they start charging excess weight fees.

There are also three zippered compartments offering separate storage for accessories and arrow cases. Those compartments are accessible from both inside and outside the case.

This case is called the Bowtruk for a reason. This case has the best wheels in the game – sealed-bearing, roller-skate wheels that roll smooth as glass. A sturdy handle on the opposite end makes this case a dream to roll long distances, over virtually any surface. And there’s a tow strap on the face of the case that is up when the case is being pulled, which allows the archer to attach other pieces of luggage. Essentially, your bow case becomes a truck for hauling around your luggage. That’s invaluable in the airport, when you’re trying to manage a bow case, a suitcase, and a cooler with your deer antlers and cape inside.

Best Soft Case: Legend Alpha RS

See It

Pros

• Excellent padding
• Allows bow to be secured inside for transport
• Includes pockets for all bow-related gear
• Lightweight
• Holds basically any compound bow up to 33 inches axle to axle

Cons

• Not waterproof

---

Key Features

• 37 inches long by 16.5 inches high
• Three small exterior pockets, plus one exterior arrow-sized pocket
• Thick padding throughout the case
• Interior tie-downs for securing the bow inside
• Straps for carrying like a suitcase, over the shoulder or like a backpack

I’m going to be honest here. When I’m looking for a soft bow case, I’m looking for something that provides some protection, without breaking the bank. All this case needs to do is keep my bow and related gear in one place and relatively safe during normal transport from home to the club or the woods.

I treat the case and its contents with respect, but I don’t baby it. It needs to protect my bow from some rough handling.

The Legend Alpha RS perfectly fits this mold. It will hold any compound up to 33 inches axle-to-axle, with the sight attached. If you’ve got a 10-inch stabilizer or longer, you’ll have to detach it, or bring both zippers together on either side of the stabilizer, which will stick out of the case.

The padding is soft, yet durable. There’s an exterior pocket perfect for loose arrows or arrows stowed inside a hard case, plus three smaller pockets that can hold a wide range of other gear.

It’s got a shoulder strap and a handle for carrying. So it has what it needs to keep my gear organized and relatively protected from normal transportation by me. And it only costs $120.

Home run.

Best Value Soft Case: Easton Bow-Go 4118 Bow Case

See It

Pros

• It costs $60
• Will fit most hunting compounds
• Ample padding
• Multiple compartments for holding arrows and other gear
• Excellent value

Cons

• Not waterproof

---

Key Features

• Holds any bow up to 41 inches in overall length
• 18 inches from top to bottom
• Four total pockets for arrows and other gear
• Extra thick front to back to allow you to store your bow with quiver attached

The Easton Bow-Go 4118 is a new, budget-friendly soft case from Easton that checks all the right boxes for a soft case – including a pricetag of $60. This is the case you’re going to use simply to keep your bow and other gear in one place, and to transport your bow to and from the field or range inside your vehicle.  In other words, you’re not expecting this case to provide serious impact protection.

This case will hold compound bows up to 41 inches in total length, and it’s 18-inches deep. You can leave your sight on the bow inside this case, but if you’ve got a stabilizer over 8 inches long, count on having to remove it. Or, you can do what I do, and leave the stabilizer on, allow it to protrude above the case, and use the two zippers to zip up the case on either side of the stabilizer. Everything will be secured inside, but your stabilizer will stick out.

An exterior pocket is sized perfectly to carry arrows and/or any size hunting or target stabilizer. Three other exterior and interior pockets are ideally sized for all other gear you might need on the range or in the tree stand.

Best for Air Travel: SKB ATA Double Bow Case

See It

Pros

• Lots of interior space
• Plenty of padding
• Built-in locks
• Solid wheels

Cons

• Not the lightest airline-worthy case

---

Key Features

• 45 inches long by 20 inches tall by 8 inches deep
• Made from the same grade material – molded polyethylene – specified by the U.S. military for cases and containers
• Capable of holding two compound bows
• TSA locks built into two of four latches
• Lifetime warranty
• Foam towers securely hold a dozen arrows
• Weighs 21 pounds

The SKB ATA Double Bow Case gets my nod as the best bow case for airline travel, because this is the case I’ve been using for all my hunts over the past decade or so. It’s been to the Arctic in winter, to south Texas, to the plains of Wyoming and to other destinations, and it’s still ticking. I know this case can take abuse, because I’ve seen the abuse it’s taken. And when you fly with a bow case, count on that case being abused. It’s as sure as death and taxes.

What separates the ATA Double Bow Case from others – besides its military-grade construction – is its simplicity. Inside the case there’s a floor padded with eggshell foam, padded columns attached to the back to hold a dozen arrows, and a removable eggshell-foam mat that serves as a divider. And that’s it.

From my experience, this simplicity allows you to stuff in as much gear as you want, the way you want. The normal airline weight for baggage before overweight fees are charged is 50 pounds. When I go on a hunt, I’m getting every piece of checked luggage as close to 50 pounds as possible.

The ATA Double Bow Case has plenty of room for your bow and lots of other gear. Stuff things around your bow, put the divider on top to protect your bow and then pack in lots of other stuff until you hit 49.9 pounds total weight.

The built-in TSA locks make life simple, and the wheels are sturdy, yet roll freely. The “lifetime warranty” is for real. Two latches on my case were broken on one of my trips, and SKB sent me two new ones for free to replace them. It’s an excellent bow case for sure, but with airline baggage limitations today, it’s also an excellent piece of luggage, which is key for getting all the gear you need to a distant destination.

​Best Budget: Plano 110 Protector Series Compact Bow Case

See It

Pros

• Costs $60
• Lockable
• Can protect your bow from a fair amount of rough handling
• Arrow storage in the lid
• Velcro straps lock your bow to the foam bed

Cons

• Not airline worthy
• Bulkier than a soft case

---

Key Features

• Measures 43 inches by 19 inches by 6.75 inches
• Four latches and two ring tabs for installing locks
• Interior pillars keep the case from collapsing on top of your bow
• Thick padding
• Made of sturdy plastic

Soft bow cases are nice for simple transportation to and from the range or field, but sometimes you need just a little extra protection for your bow. Maybe you want to toss your bow into the bed of the truck, where it has to share space with tools, mowing equipment, etc. that potentially could bang into it.

The Plano 1110 Protector Series Bow Case is the perfect case for these situations, and when you don’t want to pay for a high-end case with all the bells and whistles. This is your basic, plastic case. Strap your bow to a foam bed, stash your arrows into the lid-mounted arrow holders, close the latches and go.

At 43-inches long, it’s going to hold basically any modern compound bow on the market today.

You’re not taking this case on an airplane. You just want something to protect your bow from rough conditions, without having to break the bank.

​Best for Crossbows: Tarantula Echo Crossbow Case

See It

Pros

• Fits most standard, narrow, and reverse-draw crossbows
• Lots of storage
• Backpack straps

Cons

• Probably won’t fit all crossbows

---

Key Features

• Dimensions: 39 inches x 24 inches x 10 inches
• Four accessory pockets, plus an arrow pocket that holds bolts up to 24 inches long
• Decent padding
• Two carry handles plus shoulder strap

Before we describe the Tarantula Echo, let’s acknowledge that many crossbows – especially the high-end ones from Ravin and TenPoint – come with their own cases when you buy them. Also, for serious travel, SKB has some excellent crossbow cases in its iSeries lineup, but they’re model-specific. The SKB TenPoint TRX 515 Case is only meant to be used with that bow, so if you’ve got a Mission Sub-1, you need a different case.

What we looked for in our “best crossbow case” is a case that almost anyone could buy to fit almost any crossbow. We’re assuming you have a crossbow, but you don’t have a case.

The Tarantula Echo is a case that will fit most crossbows out there – especially most newer crossbows. Older crossbows are the ones where you might find some fitment issues. It will fit standard-design crossbows, reverse-draw crossbows, and super-narrow crossbows.

It has a zippered pocket designed for holding bolts up to 24 inches long and multiple exterior pockets to organize and stow other small pieces of gear.

The Echo has handles on both sides of the case, so you can carry it left- or right-handed, and it has nice shoulder straps so you can carry your crossbow case like a backpack. The zippers are heavy duty, which might not seem like a big deal, except these are extra-long zippers running nearly the whole way around the case. When big zippers are cheap, they separate in no time. These will stand the test of time.

Best Honorable Mention: Pelican 1745 Air

See It

PROS

• Durable
• Secures your bow inside
• Airline grade
• Includes features to organize your gear inside

CONS

• Expensive

FEATURES

• Padded bow blanket
• Foam arrow holders
• Waterproof
• Excellent wheels
• TSA-approved latches

The Pelican Air isn’t one of our picks for “best” in the various categories we’ve chosen, but you can’t talk about “best bow cases” without mentioning it. It’s definitely one of the best.

For decades, Pelican has been the industry leader in building cases to protect delicate electronic gear, especially camera equipment. They took that know-how and built the Pelican Air bow case. It’s a hard plastic case that’s sturdy enough for airline use. With 44 inches of interior width, 17 inches of depth and 8 inches of height, this case is a tank. It can take a beating, whether it’s bouncing around in the back of a pickup bed, on the floor of a johnboat, or on its way to the belly of an airplane.

The floor of the case where you store your bow features movable foam pads, so you can protect the parts of your bow that need extra padding. It also has movable straps to secure your bow to the floor. Once you secure your bow, you can Securely cover it with a bow blanket that protects your bow from anything else you might pack inside the case.

The Pelican Air has six push-button latches–two of which feature TSA-approved locks. These are handy, because they allow TSA agents to open your case for inspection in the airport without having to call you for keys.

The wheels on the Pelican Air are pinned tightly in place at one end of the case. That minimizes the chances of them snagging in transportation and separating from the case. And don’t worry about water or dust getting inside the Pelican Air. When latched, this thing is sealed tightly, thanks to a rubber O-ring lining the case’s edges.

Mystery Ranch Anchor Point Bow Case

See It

Pros

• Can fit a 34-inch bow with 10 inch stabilizer and bow quiver mounted
• Sleek, with plenty of storage 
• Good protection for car travel 

Cons

• Not for air travel 

---

Key Features

• Dimensions: 21 x 39.5 x 9.25 inches
• Weight: 5.6 pounds
• Fits bows up to about 34 inches axle to axle (depending on cam size)
• Internal accessory pockets
• Large external pocket (can fit 32-inch arrows)
• Internal quiver and arrow storage pocket
• Fully padded
• Made from 840D ballistic carbonate coated nylon
• YKK zippers
• Price: $300

I’ve used a lot of soft bow cases and I haven’t liked any of them until I got my hands on the Anchor Point. The difference is the Anchor Point’s exterior is sleek so there’s no clumsy buckles or snag points as you slide it in and out of your car. Yet it still has all the organizational pockets you need to carry release aids, stabilizers, tools, arrows, a rangefinder and more. 

My favorite thing about the Anchor Point is that I can put my 34-inch bow into the case with the stabilizer attached. Nothing is more annoying than having to unscrew a stabilizer and then reinstall it, so that’s a welcome feature. I can even keep my bow quiver on if I’m in a rush. Or I can pop off the quiver and put into the internal arrow chamber, which fits my full length arrows (32.5-inch draw length). The external long pocket is also long enough to hold full-length arrows if you want to carry spares. 

This is a bow case that will keep your gear organized and protected while you’re headed out on a hunt or going to the range. Even though it’s a durable and protective case, it’s not going to keep your bow safe from airline baggage handlers. You’ll want a hard sided case or a soft case with a rigid frame for air travel. —Scott Einsmann

Best for Hunting: Sitka Nomad

See It

Pros

• Tons of storage 
• Can carry a bow, arrows, gear, and clothing 

Cons

• Easy to pack over 50 pounds

---

Key Features

• 8600 cubic inches
• Dimensions: 42 x16 x14 inches
• Wheeled
• Telescoping handle
• Interior zipped lid pocket
• Top accessory zippered pocket
• Internal compression straps

If I’m not hunting, I can travel with just a small carry-on bag, but even a three-day turkey hunt requires a ton of gear. Good luck fitting a vest, calls, boots, Permethrin, Thermacell, and hunting clothes into a carry-on. That’s why I’ve been flying with a Sitka Nomad lately. I’ve taken it waterfowl hunting in eastern Colorado, to the Lancaster Archery Classic, turkey hunting in Nebraska, and to the 2023 Outdoor Life gun test. With thousands of air miles on the bag, I’m sold that it’s the perfect piece of hunting luggage. 

The interior of the Nomad is a lot like a duffel—a large empty space that you can fill with gear. No useless compartments or space-hogging pockets. One of the key things that make the Nomad better than a duffel bag is its rigid frame and wheels. The rigid frame provides enough protection to use the Nomad as a bow case. I strap a bow to the bag using the compression straps and then pack clothing around it for added protection. 

You can easily fit all the gear and clothing you need for a seven-day hunt into the Nomad, but you can pretty easily pack it over 50 pounds. I’ve found if I pack it full of clothing and some gear, it will hit 50 pounds. So with a bow and a lot of gear, I pack some clothing in the Nomad and the rest in a carry-on. 

Aside from it being easy to push the oversized baggage limits, the other cons I’ve experienced is that the zipper is sticky. Both are manageable cons and are outweighed by the Nomad’s functionality. – Scott Einsmann

Things to Consider When Buying a Bow Case

Fit

Not all bows fit in all cases. With compound bows, for example, some are too long or too wide for certain cases. Make sure the case you’re considering is long and wide enough to carry your bow.

Ideally, you’ll also want some wiggle room. A bow is not something you want to have to force inside a case and then shut it quickly before it pops out. Pressure on a bowstring is never a good thing, regardless of the type of bow.

Purpose

If you’re only driving with your bow from home to your hunting spot, then you don’t need a case that’s suited for airline travel. But if you plan to fly to distant hunting destinations or do some adventure bowhunting, then you don’t want a case that’s only designed to carry your bow in the back of your truck.

And be honest with yourself. If you tend to be hard on equipment, get a case that can withstand your lifestyle. A cheap plastic case bouncing around in the back of the truck with the spare tire, gas can, tire iron, and chainsaw probably isn’t going to survive too many rides. When the case fails, your bow is in danger.

Presumably, you are buying a case to protect your bow. So think about what you’re protecting it from and choose accordingly.

Capacity

What do you want your case to hold? If you just need to store your bow, then you don’t need a ton of extra space or pockets. But if you want your bow case to hold everything associated with shooting that bow, that’s a different story. You need more space and organizing pockets for release aids, finger tabs, field points, broadheads, stabilizers–the works.

A lot of bowhunters want their bowhunting backpack and bow case sitting by the door ready to go, without wondering if the release is in there, or the quiver. If the bow case is where everything lives, you need room to store it all.

I have one bow case that I use only for airline travel. It’s a big case that can hold my compound bow, all my related shooting gear, plus clothes and other items. I need that case to be large and roomy for a specific reason.

FAQs

Q: How much does a bow case cost?

Bow cases usually cost anywhere from $50 to several hundred dollars, depending on the material used and added features. You definitely get what you pay for when it comes to bow cases, but there are options that can fit your needs without breaking the bank. 

Q: Should I choose a hard case or a soft case?

Choosing a hard case or a soft case comes down to personal choice, but practicality should also guide your decision. Hard cases offer more protection against hard knocks, but they’re bulky and cumbersome to carry. Soft cases are portable and easy to maneuver inside a vehicle with other gear, but lack the extra protection of hard cases. If you do a lot of long distance traveling, you’ll want to invest in a hard case. If you just need something to make sure it doesn’t slide around in your truck, a soft case is the way to go.

Q: Can I take a bow on an airplane?

While you can’t stash it in a carry-on, you can definitely fly with a bow. You just have to transport it as checked luggage. And you’ll want to invest in a case that’s rated for air travel. Case manufacturers use different materials in airline grade cases than regular plastic ones. That’s why they are so much more expensive. But trust me, you want the strongest case on the market to protect your bow when you’re flying. The damage I have seen done to even airline grade cases over the years is astonishing. Basic plastic cases that cost $100 or so will not survive.

Final Thoughts on the Best Bow Cases

The best bow cases don’t require you to spend a small fortune, but they are something you don’t want to cut corners on. If you need top-end protection, then get it. Trust me, you’ll regret it if you don’t. If you don’t need a case for air travel, then simply consider how and where you’ll be transporting your bow and buy accordingly. Keep in mind, whatever you spend on a case is likely to pale in comparison to what you’ve invested in the contents it’s carrying.

The post The Best Bow Cases of 2026, Tested and Reviewed appeared first on Outdoor Life.

For invasive reptile hunters in Florida, there’s another predatory lizard on the radar. Nile monitors, native to Africa, are populating parts of the Sunshine State, and they can now be killed year-round without a permit or hunting license.

Mike Kimmel, the Python Cowboy, is known for targeting Florida’s least-wanted invasive species, including Burmese pythons and green iguanas. Kimmel is now also targeting Nile monitors, which he refers to as a “new and upcoming invasive species” in a new YouTube video (above). The footage includes a past clip where he wrangled a roughly six-foot-long Monitor lizard with the help of his dog, Otto.

“A Nile monitor is essentially like a smaller Komodo dragon,” Kimmel says in the video. “It’s a predatory lizard and they don’t mess around. They’re not dumb. They’re more like a python mixed with an iguana. That’s a good way to think of them.”

Kimmel owns Martin County Trapping and Wildlife Rescue, and he focuses his hunting efforts on Florida’s southeast coast. But on the west side of the state, Nile monitors aren’t exactly new. They’ve been trapped in and around Cape Coral in Lee County for around 20 years.

“In that 20-year timeframe, our environmental resources staff has caught several hundred lizards, close to 800 now,” City of Cape Coral environmental biologist Harry Phillips told Outdoor Life in an email. “There are pockets of them, but they are greatly diminished.”

Phillips says Cape Coral hosts the largest population of the striped invasive lizards in the state. The area is also home Florida’s largest population of burrowing owls. At nine inches tall, the burrowing owl is listed as threatened in Florida. They live in burrows and are active during the day. Niles have similar behaviors.

“Nile monitors have a strict carnivorous appetite,” Phillips says. “Having a predator such as the Nile monitor in Florida is a detriment to native species, and a further threat to listed species such as gopher tortoises and burrowing owls.”

Originally added to Florida’s prohibited species list in 2021, Nile monitor lizards are a semi-aquatic species that can survive on land near salt or freshwater. They eat bugs, fish, frogs, young crocodiles, birds and their eggs, as well as small mammals. They’ve also been known to attack small pets and livestock, such as chickens.

Nile monitor lizards are considered “relocated exotics” that have either been released or have escaped from captivity. They can grow up to 6.5 feet long and weigh nearly 20 pounds. They are fast runners that can reach around 18 miles an hour, and they’re strong swimmers, able to hold their breath underwater for roughly an hour. Their ability to survive in various habitats, including mangroves and marshes, has allowed them to expand through Florida’s vast canal infrastructure.

Read Next: Can You Make a Living Hunting Pythons? We Asked Florida’s Invasive Snake Contractors

“South Florida’s extensive canal system may provide dispersal corridors for the species, which tends to inhabit water edges,” states Florida Fish and Wildlife Conservation Commission in its regulatory status report. “Current efforts by FWC include actively patrolling for and removing Nile monitors from known populations and responding rapidly to sightings of monitor species in new areas.”

FWC encourages the public to report all Nile monitor sightings in the state, either by calling the agency or through an online mapping system.

The post South Florida’s Newest Invasive Threat Is a 6-Foot-Long Lizard from Africa appeared first on Outdoor Life.

 

Electrochemical CO­₂ reduction converts CO­₂ to higher-value products using an electrocatalyst and could pave the way for electrification of the chemical industry. A key challenge for CO­₂ reduction is its poor selectivity (faradaic efficiency) due to competition with the hydrogen evolution reaction in aqueous electrolytes. Rotating ring-disk electrode (RRDE) experiments have become a popular method to quantify faradaic efficiencies, especially for gold electrocatalysts. However, such measurements suffer from poor inter-laboratory reproducibility. This work identifies the causes of variability in RRDE selectivity measurements by comparing protocols with different electrochemical methods, reagent purities, and glassware cleaning procedures. Electroplating of electrolyte impurities onto the disk and ring surfaces were identified as major contributors to electrocatalyst deactivation. These results highlight the need for standardized and cross-laboratory validation of CO₂RR selectivity measurements using RRDE. Researchers implementing this technique for CO₂RR selectivity measurements need to be cognizant of electrode deactivation and its potential impacts on faradaic efficiencies and overall conclusions of their work.

Maria Kelly is a Jill Hruby Postdoctoral Fellow at Sandia National Laboratories. She earned her PhD in Professor Wilson Smith’s research group at the University of Colorado Boulder and the National Renewable Energy Laboratory. Her doctoral work focused on characterization of carbon dioxide conversion interfaces using analytical electrochemical and in situ scanning probe methods. Her research interests broadly encompass advancing experimental measurement techniques to investigate the near-electrode environment during electrochemical reactions.

 

 

The post Challenges in CO₂ Reduction Selectivity Measurements by Hydrodynamic Methods appeared first on Physics World.

Pairs of nonidentical particles trapped in adjacent nodes of a standing wave can harvest energy from the wave and spontaneously begin to oscillate, researchers in the US have shown. What is more, these interactions appear to violate Newton’s third law. The researchers believe their system, which is a simple example of a classical time crystal, could offer an easy way to measure mass with high precision. It might also, they hope, provide insights into emergent periodic phenomena in nature.

Acoustic tweezers use sound waves to create a potential-energy well that can hold an object in place – they are the acoustic analogue of optical tweezers. In the case of a single trapped object, this can be treated as a dissipationless process, in which the particle neither gains nor loses energy from the trapping wave.

In the new work, David Grier of New York University, together with graduate student Mia Morrell and undergraduate Leela Elliott, created an ultrasound standing wave in a cavity and levitated two objects (beads) in adjacent nodes.

“Ordinarily, you’d say ‘OK, they’re just going to sit there quietly and do nothing’,” says Grier; “And if the particles are identical, that’s exactly what’s going to happen.”

Breaking the law

If the two particles differ in size, material or any other property that affects acoustic scattering, they can spontaneously begin to oscillate. Even more surprisingly, this motion appears unconstrained by the requirement that momentum be conserved – Newton’s third law.

“Who ordered that?”, muses Grier.

The periodic oscillation, which has a frequency parametrized only by the properties of the particles and independent of the trapping frequency, forms a very simple type of emergent active matter called a time crystal.

The trio analysed the behaviour of adjacent particles trapped in this manner using the laws of classical mechanics, and discovered an important subtlety had been missed. When identical particles are trapped in nearby nodes, they interact by scattering waves, but the interactions are equal and opposite and therefore cancel.

“The part that had never been worked out before in detail is what happens when you have two particles with different properties interacting with each other,” says Grier. “And if you put in the hard work, which Mia and Leela did, what you find is that to the first approximation there’s nothing out of the ordinary.” At the second order, however, the expansion contains a nonreciprocal term. “That opens up all sorts of opportunities for new physics, and one of the most striking and surprising outcomes is this time crystal.”

Stealing energy

This nonreciprocity arises because, if one particle is more strongly affected by the mutual scattering than the other, it can be pushed farther away from the node of the standing wave and pick up potential energy, which can then be transferred through scattering to the other particle. “The unbalanced forces give the levitated particles the opportunity to steal some energy from the wave that they ordinarily wouldn’t have had access to,” explains Grier. The wave also carries away the missing momentum, resolving the apparent violation of Newton’s third law.

If it were acting in isolation, this energy input would make the oscillations unstable and throw the particles out of the nodes. However, energy is removed by viscosity: “If everything is absolutely right, the rate at which the particles consume energy exactly balances the rate at which they lose energy to viscous drag, and if you get that perfect, delicious balance, then the particles can jiggle in place forever, taking the fuel from the wave and dumping it back into the system as heat.” This can be stable indefinitely.

The researchers have filed a patent application for the use of the system to measure particle masses with microgram-scale precision from the oscillation frequency. Beyond this, they hope the phenomenon will offer insights into emergent periodic phenomena across timescales in nature: “Your neurons fire at kilohertz, but the pacemaker in your heart hopefully goes about once per second,” explains Grier.

The research is described in Physical Review Letters.

“When I read this I got somehow surprised,” says Glauber Silva of The Federal University of Alagoas in Brazil; “The whole thing of how to get energy from the surrounding fields and produce motion of the coupled particles is something that the theoretical framework of this field didn’t spot before.”

“I’ve done some work in the past, both in simulations and in optical systems that are analogous to this, where similar things happen, but not nearly as well controlled as in this particular experiment,” says Dustin Kleckner of University of California, Merced. He believes this will open up a variety of further questions: “What happens if you have more than two? What are the rules? How do we understand what’s going on and can we do more interesting things with it?” he says. 

The post Time crystal emerges in acoustic tweezers appeared first on Physics World.