Existence of "second sound" confirmed by Physicists

Fascinating existence of "second sound" captured for the first time

Heat usually spreads until it fades away. In everyday life, a warm spot in liquid quickly blends with cooler areas, and everything settles at a single temperature. MIT researchers, after exploring a superfluid quantum gas, have shown that heat can travel in a wavelike manner called second sound, instead of spreading out and calming down. First theorized in 1938, heat's wave-like flow through superfluid's, known as "second sound", has proven difficult to directly observe. Now, a new technique has finally done it, and could be used to study neutron stars and high-temperature superconductors.  Pantxo Diribarne from the Atomic Energy and Alternative Energies Commission and the University of Grenoble Alpes in France, sees this as a chance to unravel more mysteries about peculiar states of matter. Scientists have captured direct images of heat behaving like sound, an elusive phenomenon called 'second sound', for the very first time. Imaged within an exotic superfluid state of cold lithium-6 atoms by a new heat-mapping technique, the phenomenon shows heat moving as a wave, bouncing like sound around its container.

The strange and incredible phenomenon known as “second sound” refers to a state where heat moves like a wave, not by diffusion like we’re used to. Instead of slowly spreading out, thermal energy pulses through a material in much the same way sound travels through air. It’s not something you’d experience in everyday life, but in ultra-cold or highly ordered systems, like certain crystals or quantum fluids, second sound reveals a completely different side of how energy can move. This wave is different from how temperature typically flows. Instead of dissipating steadily until it is fully spread out, the heat pulses like ripples on a pond. It’s like heat is speaking a language we rarely get to hear. The phenomenon known as quantum turbulence comes into play when normal and superfluid components move together at large scales, then lose lockstep at smaller scales. Understanding the way that second sound moves could help scientists predict how heat flows inside ultra dense neutron stars and high-temperature superconductors, one of the "holy grails" of physics whose development would enable near-lossless energy transmission. 

A superfluid is a special liquid that moves without viscosity. In helium-4, this behaviour appears at temperatures below about −456 °F (-271°C). When the fluid is both superfluid and normal, friction between the two forms can still appear. This friction can produce swirling structures in the superfluid, but it also allows temperature pulses (second sound) to zip through. Scientists are keen to study high-temperature superconductors, which carry current with little power loss. Some say that second sound might shed light on thermal transport in these systems. Neutron stars, those incredibly dense objects in space, may also carry clues. A quantum fluid could occupy their interiors and possibly channel heat in ways that match second sound patterns. "It's as if you had a tank of water and made one half nearly boiling," study co-author Richard Fletcher, an assistant professor of physics at Massachusetts Institute of Technology (MIT), said. "If you then watched, the water itself might look totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks totally still." Typically heat spreads from a localized source, slowly dissipating across an entire material as it raises the temperature across it. But exotic materials called superfluid's needn't play by these rules. Created when clouds of fermions (which include protons, neutrons and electrons) are cooled to temperatures approaching absolute zero, atoms inside superfluid's pair up and travel frictionlessly throughout the material.

Researchers tested second sound in helium to see if the same wave idea appears in other exotic materials. Discovering a pattern in superfluid helium might help interpret signals in advanced physics experiments. With second sound, the puzzle of how energy flows becomes more precise. This clarity supports efforts to design technologies which harness quantum effects, like sensitive sensors or more efficient cooling systems. The team used new imaging approaches to watch heat pulses bounce through the fluid. By capturing that movement, they separated normal heat spread from the heat wave which never truly mellowed. Data analysis indicated that the speed of these waves is roughly 49 feet/s (15 meters/s) for helium at 1.6 K, though slight changes in temperature and pressure can shift that speed. The wave eventually diminishes, but it travels long enough to confirm a distinct second sound. Heat flows differently through the material: instead of spreading through the movements of particles within the fluid, as it typically flows, heat sloshes back and forth within superfluid's like a sound wave. This second sound was first predicted by the physicist László Tisza in 1938, but heat-mapping techniques have, until now, proven unable to observe it directly.

To measure second sound accurately, researchers used a resonant cavity filled with superfluid helium. This setup allowed them to create and track standing temperature waves which offered a direct glimpse into the behaviour of vortex lines and the space between them. They paired this with particle-tracking techniques using hollow glass microspheres. These tiny tracers helped capture the motion of the fluid itself, and showed how heat pulses affected surrounding particles, without disturbing the second sound signal. "Second sound is the hallmark of super fluidity, but in ultra cold gases so far you could only see it in this faint reflection of the density ripples that go along with it," study senior-author Martin Zwierlein, a professor of physics at MIT, said. "The character of the heat wave could not be proven before." To capture second sound, the researchers had to solve a daunting problem in tracking the flow of heat inside ultra cold gases. These gases are so cold that they do not give off infrared radiation, upon which typical heat-mapping, or thermography, techniques rely. Instead, the physicists developed a method to track the fermion pairs through their resonant frequencies. Lithium-6 atoms resonate at different radio frequencies as their temperatures change, with warmer atoms vibrating at higher frequencies.

Past studies tried to explain second sound by focusing on vortex lines, which are small, swirling cores in the superfluid. Recent work suggests these lines set a key spacing level where wave-like temperature movement can dominate. The surprising outcome is that friction does not single-handedly decide how heat flows. Instead, large-scale circulation and vortex tangles form a cascade that shapes when ordinary heat conduction switches to a traveling wave. Research might push second sound concepts into higher temperatures. That would bridge a gap between helium superfluid's and solid systems which show wave-like temperature travel. Critics note that temperature swings and mechanical vibrations sometimes mask delicate signals. To address this, scientists plan stricter temperature control and more refined imaging in the next generation of tests. By applying resonant radio frequencies corresponding to warmer atoms, the scientists made these atoms ring in response, enabling them to track the particles’ flow frame by frame. "For the first time, we can take pictures of this substance as we cool it through the critical temperature of super fluidity, and directly see how it transitions from being a normal fluid, where heat equilibrates boringly, to a superfluid where heat sloshes back and forth," Zwierlein said.

One of the most surprising findings is that the behaviour of second sound remained nearly unchanged across different temperatures. Researchers expected the friction between fluid components to vary more significantly, but the measurements showed very little temperature dependence. This suggests that something else, possibly the structure of the fluid’s internal turbulence, plays a larger role than previously thought. This discovery opens the door to rethinking how energy is lost in quantum fluids, especially in systems where traditional viscosity doesn’t apply. The physicists say that their ground breaking technique will enable them to better study the behaviours of some of the universe's most extreme objects, such as neutron stars, and measure the conductivity of high-temperature superconductors to make even better designs. "There are strong connections between our puff of gas, which is a million times thinner than air, and the behaviour of electrons in high-temperature superconductors, and even neutrons in ultra dense neutron stars," Zwierlein said. "Now we can probe pristinely the temperature response of our system, which teaches us about things that are very difficult to understand or even reach." If second sound ideas link to superconductors, we might improve next-gen energy lines. Some also dream of applying wave-based cooling in labs. On cosmic scales, linking superfluid features to neutron star interiors could hint at how these stars shed energy. Tracking those waves might lead to fresh insights into the behaviour of matter under crushing forces of gravity. Even though heat normally spreads until it dies down, the phenomenon of second sound defies that notion. Scientists are now exploring how temperature pulses might drive new physics in quantum fluids and even in cosmic bodies.

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Development of High-End 3nm GAA Chips by Huawei

 Huawei expected to chips away at US tech and trade barriers with Development of High-End 3nm GAA Chips by 2026

The tech and trade tension between the US and China has been growing for years, leading more recently to the introduction of far-reaching trade sanctions and restrictions by the US which in turn, led to a surge in tech investment and development in China as Sino companies find themselves increasingly unable to source the technology hardware and software upon which they previously relied. Chinese companies find a new way to work around these restrictions. In a major move, Huawei plans to develop a high-end node for the domestic chip industry, the 3nm GAA, which would put the Chinese firm in a competitive position. Following are the some of the important points:-

Chinese tech firms like Huawei, appear to take a step forward in any one key technology area, the US administration applies a fresh turn on the trade restriction ratchet to block or slow its progress

China appears to be catching, matching or swerving around the US and European technology that it’s been forbidden to import in order to meet its AI and general IT industry ambitions

Will this US whack-a-mole tactic work for the longer term? There is the state of play in three key areas of the Sino/US tech and trade struggle

There's no doubt that Huawei is emerging as one of China's most dominant companies in innovating and adjusting product portfolios to compete with Western alternatives. The firm has a deep-rooted business, not just in the mobile segment, but also in AI and computing, making it a force not to be reckoned with. It is being claimed that Huawei has initiated R&D work for 3nm GAA, after the company's success with the Kirin X90 SoC which employs a domestic 5nm process from SMIC. It might had a negative impact on the sales (and growth potential) of many US companies which have traditionally done a lot of business in China and are now trying to find ways in which they can continue to retain relevance and market share in China without breaking the rules. Apple is the latest company coming under scrutiny for the relationship it has developed with China’s Alibaba to add AI features to iPhones sold in the world’s second most populated country. 

The report claims that Huawei is going to opt for the GAA (Gate-All-Around) route with 3nm, and the firm is said to be moving away from traditional silicon designs for its transistor channels to employing "two-dimensional" materials, which is an approach not used for this particular node size. This could allow better performance at a smaller scale and lower power consumption than traditional silicon-based designs. Interestingly, a GAA-focused design for 3nm has only been done by Samsung Foundry for now, so could there be a potential collaboration with Huawei? In terms of individual companies, the main mole that the US has been (and still is) trying to whack is Huawei, which has been forced to develop its own smartphone operating system and processors and revamp its operations in recent years and, if its latest annual financial results are anything to go by, it has more than weathered the storm. As part of its response to trade pressures, it seems, Huawei has invested a great deal of resources in trying to develop high-performance AI chips to counter the global dominance of US chip specialist Nvidia. Also in play here is the ‘buy China’ push by the Chinese government to massively boost the development and production of domestic silicon chips in the face of rising trade tensions and the high probability of further trade restrictions by the US.

Apart from this, Huawei is also developing a "carbon-based" 3nm design, which will feature carbon nanotubes, an alternative to silicon-based transistors and interconnects. So, it is safe to say that Huawei will likely test out a new approach, collaborating with China's biggest foundry, SMIC. Currently, these plans are in the initial stages, and Huawei is known to have come up with optimistic plans. However, with the company's success in the 5nm segment, especially when it comes to integrating the node into a consumer product, it wouldn't be wrong to say that we should expect more advancements. To counter the Chinese effort, particularly in relation to very advanced AI chips, the US and its allies have impeded Chinese efforts to procure the equipment and expertise necessary to develop advanced EUV (extreme ultraviolet lithography)-enabled silicon used by Nvidia and largely responsible for its current dominance. Huawei decided to develop its own Ascend high-performance chips, not based on advanced lithography but on the older 7 nanometre process technology to which it would apply fancy footwork and innovation to try to catch up. The progress of this effort, which involves the development of its own chip fabrication plants, is currently at the centre of the China/US tech and tariff struggle. 

Earlier, Huawei said it had begun “mass shipping” the much-anticipated Ascend 910C AI training chips, which first made the headlines. These are deemed fast and powerful enough to approach the sort of performance (and, crucially, the low power consumption) achieved by Nvidia and its H20 chips, when deployed as a multichip system. Huawei is emerging as a key player in the region, and the firm has managed to vertically integrate the supply chain to the point where it can now compete with the West in terms of technological superiority. Interesting times are ahead of us, especially considering the US-China technological balance. Hot on the heels of the ‘C’ is the Ascend 910D, due later in May, with mass production planned for the last quarter of this year. Its theoretical peak performance is cited as 1.2 petaflops (PFLOPs) which, if true, would surpass Nvidia’s H100.

Until very recently Nvidia was still allowed to sell its H20 chips into China and to its allies, since the chips were deemed powerful enough for AI model training but not powerful enough to enable very advanced applications (such as those that might guide missiles in real time). The H20 has proven popular with Chinese customers, such as Alibaba, Bytedance and Tencent. But the US authorities decided to do a spot of rule tightening and effectively banned the sale of H20 chips into China, much to the chagrin of Nvidia, which announced in a filing with the Securities and Exchange Commission (SEC) that, as a result of that restriction, it will report charges of up to $5.5bn related to “H20 products for inventory, purchase commitments, and related reserves”.  So with the Nvidia H20 mole whacked, the path was clear for Huawei to drum up a considerable amount of business in China if it could match Nvidia’s cost and performance levels and produce enough products to meet demand, especially as the demand for AI workloads has ramped up significantly in China since the launch of the R1 large language model (LLM) by China’s Deepseek. In terms of capabilities, Huawei seems to be exceeding many expectations. 

Adopting more advanced process technologies for the chips is undoubtedly required if China (probably led by Huawei) is to continue the game of tech catch-up to enable its AI capabilities. To that end, Nikkei Asia reports that China bought a record amount of chip-making equipment in 2024 to build up stockpiles of key tools in order to plump up its chip-making capabilities, buying nearly $20bn worth of kit from the Netherlands and Japan alone, along with purchases from Malaysia and Singapore. According to Canada’s WCCF Tech site, the Ascend 910C is believed to be almost on par with Nvidia’s popular H100. And at the system level, things look even better for Huawei, with one analysis reportedly finding that Huawei’s CloudMatrix CM384 solution, which integrates 384 Ascend 910C chips across 16 racks, out-performed Nvidia’s equivalent solution. So in terms of overall processing costs, the Ascend 910C appears  to have put Huawei’s AI chip effort into the Nvidia performance ball park from where it may eventually produce a viable alternative AI environment for China and its technological allies. Providing, of course, that the mole whacking doesn’t prevent it advancing in allied areas… which brings us back to EUV.

Chinese chip-makers are looking to expand in both chip manufacturing and chip packaging to meet surging local demand. Machines for silicon bonding, lithography and cleaning are being sought and the spending is a clear indicator of chip plant expansion. China’s share of the ‘mature’ chip market is projected to rise steeply in response to the Chinese government’s ‘buy China’ policy, up from 28% in 2025 to 39% by 2027. But while China’s ‘mature’ chip market looks set to boom, the US government-inspired restrictions are set to continue mole-whacking when it comes to the crown jewel of advanced EUV technology, which is supplied exclusively by Dutch company ASML. The company is prevented from selling its most advanced chip-making tools, such as Extreme Ultraviolet (EUV) lithography machines, to Chinese companies due to on-going export restrictions imposed by the Dutch government under pressure from the US. However, ASML is allowed to continue selling its older-generation deep ultraviolet (DUV) machines to China. The third key area is software. Here Huawei and China are making slow but steady progress in breaking with the US, and a significant milestone was reached when Huawei announced its latest laptop would be running on Harmony, the operating system it developed to replace Microsoft’s Windows. HarmonyOS has been in development for five years now and already powers Huawei’s smartphones and tablets. This is the first laptop to exclusively run HarmonyOS speaks to the difficulty of suddenly creating a brand new operating system, it can be a relatively slow process. Huawei says there are around 300 third-party apps available with 2,000 in development. But China’s greatest software breakthrough no doubt came with the sudden arrival of the aforementioned Deepseek R1 generative AI (GenAI) model, which illustrated how China’s IT sector appears to be thriving despite Washington’s efforts to slow it down. 

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