Continuous Cold: The Patent-Pending 500 mK Phase Separation Refrigerator
The team at Zero Point Cryogenics has invented a new mechanism for continuous cooling below 800 mK – the first new mechanism invented in sixty years. ZPC’s Patent-Pending Continuous Cold 500 mK systems leverage phase separation in a novel way to reach this temperature range efficiently. The unique entropic properties of liquid helium cause a mixture of helium-3 and helium-4 to separate into two distinct phases. While dilution refrigerators have historically used this effect to create cooling by varying helium-3 concentration across a phase boundary, our Phase Separation Refrigerator takes a different approach—providing a relatively pure helium-3 surface that can be continuously pumped on. This breakthrough offers an affordable method for accessing these temperatures, with promising applications in the field of quantum computing, quantum hardware, quantum sensing, and cryogenic research.
How does it work?
Like many refrigeration units, our new Phase Separation cryostat relies on evaporative cooling—the same process our bodies use to cool down on a hot, sunny day. This cooling method takes advantage of the equilibrium between a liquid and its vapor phase: molecules continuously evaporate from the liquid surface while others condense back into the liquid. The partial pressure of the gas above the liquid surface is known as the vapor pressure, which varies for different substances, including helium-3 and helium-4.
Evaporation is an endothermic process, meaning it absorbs energy from the liquid, leading to a net cooling effect. By continuously pumping out the vapor above the liquid, we disturb the thermal equilibrium, driving further evaporation and deeper cooling. In traditional 1 K cryostats, this process is typically performed with helium-4, which can achieve base temperatures as low as 1.4 K or even 0.9 K, as seen in our Continuous Cold 1.4 K and 0.9 K cryostats. If helium-3 is used instead, its lower vapor pressure enables even colder temperatures—potentially down to hundreds of millikelvins. However, the extreme cost and scarcity of helium-3 make this approach impractical for most applications.
Our novel Phase Separation cryostat overcomes this limitation by leveraging a unique property of helium-3 and helium-4 mixtures, as seen on the phase diagram below. Below 900 mK, the mixture phase separates into two distinct superfluid layers, with helium-3 forming a concentrated phase that floats atop the helium-4-rich phase. Since evaporative cooling relies on pumping vapor from the surface, this configuration means that helium-3 is preferentially removed, enabling the system to reach base temperatures approaching that of a pure helium-3 mixture, despite the inhomogeneous mixture.
Figure 1: Phase Diagram Frank Pobell (1995)
In theory, a system that operates with pure helium-3 will have a higher cooling power and lower base temperatures than the phase separation system. However, the scarcity and cost of helium-3 make the continuous cold cryostat an excellent tradeoff for practical applications. By efficiently using a small volume of helium-3, our system achieves base temperatures below 500 mK, providing a continuous cooling solution that balances performance with economic feasibility.
Figure 2: Model L (left) and Model I (right) Continuous Cold 500 mK systems
Key Advantages
1. Continuous Operation – Because the cooling source is the evaporation of a circulating helium-3/helium-4 mixture, there is no cycle/regeneration time at base temperatures. The phase separation cryostat provides continuous cooling at 500 mK without requiring a dilution refrigerator or a large volume of helium-3.
2. Fast Cooldown and Sample Turnaround – The cooling cycle starts quickly with an optimized precooling setup that allows the system to reach the condensation stage quickly. Once it starts condensing, the helium-3/helium-4 mixture condenses primarily through helium-4, allowing it to start at a higher temperature than a pure helium-3 fridge. This leads to rapid cooldown and fast sample turnaround times of under 12 hours, making the system highly efficient for repeated use.
3. High Cooling Power – Thanks to the low vapor pressure of helium-3, the system delivers exceptional cooling power. At an operating temperature of 600 mK, the cooling power reaches approximately 1 mW, ideal for applications in quantum computing with large electronics and cable requirements.
4. Cost-Effective Cryogen Usage – The system operates with a minimal volume of helium-3—just 2 L for both our Model L and Model I systems. In contrast to traditional dilution refrigerators and helium-3 cryostats, which can require up to 40 L, ZPC’s systems significantly lower the costs of ownership and scalability.
5. Patent-Pending – ZPC has submitted patents for this technology in Canada, the US, the EU, and globally, ensuring that the Phase Separation Refrigerator technology remains uniquely available through us.
Customization
Like all ZPC products, the Continuous Cold cryostat can be customized to fit your research goals. Whether designed in our traditional Model L form factor or our novel inverted Model I, the phase separation cryostat is compatible with DC and RF wiring, optical access, superconducting magnets, and more. Connect with our sales team to discuss how we can meet your project needs.
Zero Point Cryogenics – Colder for Longer
Zero Point Cryogenics is an Edmonton-based company that manufactures high-end cryogenic equipment. The company is focused on designing robust and reliable dilution refrigerators for our customers that will satisfy their space, size, and operation requirements. By creating the world’s most reliable dilution refrigerator, ZPC customers can focus on developing their quantum technologies instead of operating their refrigerators.
For more information, visit zpcryo.com. Media contact 1-833-936-2225 or email info@zpcryo.com.