Room temperature is about 300 kelvin. Liquid nitrogen is 77. Liquid helium is 4.2. Outer space, warmed by the afterglow of the Big Bang, sits at 2.7. The machine at the centre of this week's agreement is designed to reach 0.02 kelvin — roughly a hundred times colder than interstellar space, and about as cold as anything in the known universe gets outside a laboratory.
On 24 September 2026, under the Technology Development Fund (TDF) scheme, the DRDO signed its first high-value deep-tech project agreement with a start-up — Zero mK India Private Limited of Alwar, Rajasthan — for the indigenous development of a 20 millikelvin dilution refrigerator for quantum applications. It is the first high-value agreement under the ₹500 crore corpus approved by Raksha Mantri Rajnath Singh for deep-tech and cutting-edge projects. The project is being mentored by the Director of the Solid State Physics Laboratory (SSPL) and his team.
How you get to twenty millikelvin
Ordinary refrigeration uses evaporation: a liquid evaporates, the molecules that leave carry away the most energy, and what remains is colder. Your refrigerator and your skin both work this way.
That method has a floor. As a liquid gets colder its vapour pressure collapses, so fewer molecules leave, so the cooling weakens. Pumping on liquid helium-4 gets you to roughly 1 kelvin and pumping on the rarer isotope helium-3 to around 0.3 kelvin, and there evaporative cooling effectively stops.
A dilution refrigerator gets past that floor using a genuinely strange property of helium mixtures, and the mechanism is worth understanding because it is elegant.
Below about 870 millikelvin, a mixture of helium-3 and helium-4 spontaneously separates into two phases, rather like oil and water. A concentrated phase, almost pure helium-3, floats on top of a dilute phase, which is mostly helium-4 with about 6.6 per cent helium-3 dissolved in it. That 6.6 per cent is the crucial number: it does not fall to zero even as the temperature approaches absolute zero.
Now the trick. Moving a helium-3 atom from the concentrated phase into the dilute phase is thermodynamically like evaporation — the atom moves from a dense liquid into something that behaves like a gas dissolved in the helium-4 background — and, like evaporation, it absorbs heat from the surroundings. But because the dilute phase always retains that 6.6 per cent of helium-3 however cold it becomes, the process does not shut down at low temperature the way evaporation does. It keeps working.
The machine therefore continuously pumps helium-3 across the phase boundary in the mixing chamber, distils it out of the dilute phase in the still at around 0.7 kelvin, and returns it through a heat exchanger network to go round again. A pulse-tube cryocooler does the bulk cooling from room temperature down to about 3 kelvin; the dilution circuit takes it from there to below 10 millikelvin, and holds it there indefinitely.
Why a qubit needs this
The reason is thermal noise, and it comes down to one comparison.
A quantum bit stores information in the difference between two energy states. To use it, the qubit must stay in the state you put it in. But everything at a temperature above absolute zero is jostled by thermal energy, of order kT — Boltzmann's constant times the temperature. If kT is comparable to the energy gap between the qubit's two states, the environment will simply knock the qubit from one to the other at random, and the stored information is gone.
So the requirement is that kT must be far smaller than the qubit's energy splitting. For superconducting qubits, whose transition frequencies sit in the microwave range of a few gigahertz, that condition is met at around 10 to 20 millikelvin and not much above it. This is why the number in the agreement is 20 mK and not, say, 1 K: it is set by physics, not by ambition.
There is a second reason, specific to this qubit family. Superconducting qubits are built from circuits that must actually be superconducting — zero electrical resistance — and superconductivity in the relevant materials requires low temperature in its own right. Resistance would dissipate energy and destroy the quantum state directly.
The general phenomenon being fought is decoherence: the loss of a quantum state's delicate phase relationships through interaction with the environment. Cooling does not eliminate decoherence; it buys coherence time, the window in which a computation must finish. Everything else in a quantum computer — shielding, filtering, materials, error correction — is an attempt to widen the same window. The wider architecture of India's quantum programme is set out in our explainer on the National Quantum Mission, and the security dimension in our piece on C-DOT's Q-VIKRAM and Q-AMOGH.
Why the refrigerator is the strategic item
It would be easy to treat cooling as plumbing — the boring part, next to the qubits. That inverts the actual difficulty.
Dilution refrigerators are made by a very small number of firms worldwide. They are expensive, they are slow to deliver, they require helium-3, which is itself scarce and produced largely as a by-product of tritium decay, and they are precisely the kind of enabling equipment that becomes unavailable when export controls tighten. A country that designs excellent qubits but must import the machine to cool them has not achieved an independent capability — it has achieved a dependency with extra steps.
The release names this directly: the objective includes reducing dependence on imported cryogenic infrastructure. That is the strategic content of the announcement, and it is a better answer to "why does this matter" than anything about quantum computing's eventual applications.
The same logic recurs across deep technology, and it is worth carrying as a general principle: the bottleneck is usually the tool, not the idea. Semiconductor capability is gated by lithography equipment; quantum computing is gated in part by cryogenics; advanced materials are gated by characterisation instruments. Capability in the enabling machine is what makes capability in the application durable.
The Technology Development Fund
TDF is a DRDO scheme, executed by DRDO under the Ministry of Defence, which funds Indian industry — with an emphasis on MSMEs and start-ups — to develop defence technologies that do not currently exist domestically. The developer builds the system; DRDO provides funding and technical mentoring, in this case through the Solid State Physics Laboratory.
Two features are worth noting against the procurement categories we covered earlier this week.
First, TDF is development funding, not procurement. It pays for the technology to be created. Whether the resulting product is then bought is a separate decision taken under the Buy categories described in our piece on the SAT-SAAW contract and Buy (Indian-IDDM). Development and procurement are distinct stages with distinct rules, and conflating them is the commonest error on this topic.
Second, TDF exists because of a specific market failure. A small firm cannot fund the development of a system with one probable customer, an uncertain order, and a long development cycle — no commercial lender will carry that. Either the state funds the development or the technology is not developed domestically at all. This sits alongside the Make categories and iDEX as instruments aimed at the same gap from different angles, and the wider reform of DRDO's financial powers is covered in our explainer on the DFP-2026 reform.
That the first high-value agreement under a deep-tech corpus has gone to a start-up in Alwar rather than to an established defence firm is the part of this announcement most worth remembering. Whether the machine gets built is the test; the signal is what the mechanism is now willing to fund.
🔑 Revision block
- The agreement: 24 September 2026 — DRDO's first high-value deep-tech project agreement with a start-up under the Technology Development Fund (TDF) scheme
- Partner: Zero mK India Private Limited, Alwar, Rajasthan
- Item: indigenous 20 millikelvin dilution refrigerator for quantum applications
- Corpus: first high-value agreement under the ₹500 crore deep-tech corpus approved by Raksha Mantri Rajnath Singh
- Mentoring: Director, Solid State Physics Laboratory (SSPL) and team; Defence Secretary and Chairman DRDO Rajesh Kumar Singh
- Temperature scale: room temperature about 300 K; liquid nitrogen 77 K; liquid helium 4.2 K; cosmic microwave background 2.7 K; target 0.02 K (20 mK)
- Evaporative cooling floor: about 1 K pumping on helium-4; about 0.3 K pumping on helium-3
- Phase separation: below about 870 mK, a helium-3/helium-4 mixture separates into a concentrated phase (nearly pure He-3) and a dilute phase (He-4 with about 6.6 per cent He-3)
- The cooling mechanism: moving He-3 across the phase boundary into the dilute phase absorbs heat, like evaporation — and does not shut down at low temperature, because the dilute phase retains about 6.6 per cent He-3 however cold it gets
- Components: mixing chamber (final cooling), still (He-3 distilled out at about 0.7 K), heat exchangers, and a pulse-tube cryocooler for the stage from 300 K to about 3 K
- Why qubits need it: thermal energy of order kT must be far smaller than the qubit's energy splitting; superconducting qubits work at about 10-20 mK; superconductivity itself also requires low temperature
- Decoherence: loss of quantum state through interaction with the environment; cooling buys coherence time rather than eliminating decoherence
- Strategic point: reduces dependence on imported cryogenic infrastructure; helium-3 is scarce, produced largely from tritium decay
- TDF: DRDO scheme funding Indian industry, especially MSMEs and start-ups, to develop technologies not available domestically — development funding, not procurement
🎯 Practice MCQs
Q1. A dilution refrigerator achieves millikelvin temperatures by exploiting: (a) The Joule-Thomson expansion of nitrogen (b) Phase separation in a helium-3 and helium-4 mixture (c) Magnetic levitation of superconductors (d) Laser cooling of trapped atoms
→ (b) — below about 870 mK the mixture splits into two phases.
Q2. In the dilute phase of the mixture, the helium-3 concentration approaches approximately: (a) 0 per cent (b) 25 per cent (c) 50 per cent (d) 6.6 per cent
→ (d) — and it does not fall to zero however cold the mixture becomes, which is why the cooling continues.
Q3. Evaporative cooling cannot reach millikelvin temperatures because: (a) Helium solidifies before then (b) The vapour pressure collapses as temperature falls, so the cooling weakens (c) It requires a magnetic field (d) The liquid becomes superconducting
→ (b)
Q4. Superconducting qubits typically operate at about: (a) 4.2 kelvin (b) 77 kelvin (c) 10-20 millikelvin (d) 1 kelvin
→ (c) — set by the requirement that kT be far below the qubit energy splitting.
Q5. "Decoherence" refers to: (a) Loss of a quantum state's phase relationships through interaction with the environment (b) Failure of a refrigerator's compressor (c) The gradual warming of a cryostat (d) Misalignment of laser beams
→ (a) — cooling buys coherence time rather than eliminating it.
Q6. The component of a dilution refrigerator in which final cooling occurs is the: (a) Still (b) Pulse-tube cryocooler (c) Heat exchanger (d) Mixing chamber
→ (d) — the still distils helium-3 out of the dilute phase at around 0.7 K.
Q7. The Technology Development Fund scheme is best described as: (a) A procurement category under the Defence Acquisition Procedure (b) Development funding for Indian industry, especially MSMEs and start-ups, to build technologies not available domestically (c) A DRDO recruitment programme (d) An export promotion fund for defence products
→ (b) — procurement is a separate stage under the Buy categories.
Q8. The strategic argument for developing a dilution refrigerator indigenously is principally that: (a) Imported units are of poor quality (b) It is cheaper to build than to buy (c) Cryogenic infrastructure is an import dependency that can be cut off, gating quantum capability (d) International agreements require domestic manufacture
→ (c)
Q9. Helium-3, required by such refrigerators, is scarce because it is produced largely as: (a) A by-product of tritium decay (b) A product of natural gas combustion (c) A residue of uranium enrichment (d) An output of fusion reactors in commercial operation
→ (a)
Q10. Consider the following statements: 1. The cosmic microwave background sits at about 2.7 kelvin, warmer than the target temperature of this refrigerator. 2. TDF funds the development of a technology, while whether the resulting product is purchased is decided separately. Which is/are correct? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2
→ (c) — 20 mK is about a hundred times colder than interstellar space.
📋 How this gets asked (PYQ pattern)
Quantum technology has moved from a specialist topic to a recurring one in the NDA general ability paper, and questions come in two quite different shapes.
The physics question asks about temperature scales and cooling. Absolute zero at 0 K or −273.15 °C, liquid nitrogen at 77 K, liquid helium at 4.2 K. The kelvin scale itself is asked, and candidates who convert incorrectly lose a mark they should not.
The scheme question asks what TDF, iDEX, Make-I and Make-II each do, and who runs them. TDF and iDEX both target small firms and start-ups; the Make categories sit inside the Defence Acquisition Procedure; and all of them fund development rather than buying a product. Learning them as a group with their distinguishing feature attached is far more efficient than learning each alone.
The institution question covers DRDO's laboratories. SSPL for solid state physics, LRDE for radar, ADA for aeronautical design, DRDL for missiles, and the Ministry they sit under. Their specialisations are asked as a match-the-following.
The concept question asks what decoherence is, what a qubit is, and what quantum key distribution does. Short definitions suffice, but they must be correct definitions — a qubit is not merely "a very fast bit".
For the SSB interview, this item supports an excellent answer on self-reliance, and one that avoids the usual clichés. A candidate who says that the hard part of quantum computing for India is not the physics but the equipment that makes the physics possible — and that a country which imports its cryogenics has a dependency rather than a capability — is making an argument about industrial strategy. That is a considerably better answer than praising a technology in the abstract.
Preparing for NDA? Science questions get easier once the temperature scale, the schemes and the DRDO laboratories are each learnt as a short set. Build the base with our NDA general ability notes, follow the daily NDA current affairs, and prepare with our faculty in the upcoming Cavalier courses in Delhi.
✍️ Written by Col Vijyanat Thakur — Defence studies faculty at The Cavalier. Reviewed by the Cavalier Faculty Desk.