Microelectronics, CARE IITD

19/06/2026

❄️ Inside a Dilution Refrigerator: How Do We Reach Temperatures Below 10 mK?

In our previous posts, we explored the fascinating physics that emerges near absolute zero. But an equally intriguing question is:

How do scientists actually cool a system to a few millikelvin?

The answer is one of the greatest engineering achievements in experimental physics: the dilution refrigerator (DR).

🌡️ Why not just use liquid helium?

Liquid helium boils at 4.2 K under atmospheric pressure. Pumping on helium can lower the temperature further, reaching approximately 1.2 K, but conventional evaporation cooling eventually reaches its limit.

To go below 1 K, a completely different cooling mechanism is required.

🧪 The Physics Behind a Dilution Refrigerator

A dilution refrigerator exploits the quantum properties of a mixture of two helium isotopes:

Helium-3 ((^3)He): a fermion
Helium-4 ((^4)He): a boson

Below about 0.87 K, the mixture spontaneously separates into two phases:

🔹 A concentrated phase, rich in (^3)He
🔹 A dilute phase, where a small concentration of (^3)He remains dissolved in (^4)He

The key cooling process occurs when (^3)He atoms cross from the concentrated phase into the dilute phase. This transition is endothermic—it absorbs heat from the surroundings.

By continuously circulating (^3)He through heat exchangers and the mixing chamber, the refrigerator provides continuous cooling without relying on evaporation alone.

🏗️ A Modern Dilution Refrigerator

A typical DR consists of several temperature stages:

🟠 50 K Shield – intercepts room-temperature radiation using the first stage of a pulse-tube cryocooler.

🔵 4 K Stage– provides the initial cryogenic environment and condenses helium.

🟢 Still (~0.7 K) – selectively evaporates (^3)He, driving its circulation.

🟣 Cold Plate (~100 mK) – thermalizes experimental wiring and components.

⚫ Mixing Chamber (~5–20 mK) – the coldest point in the system, where samples or quantum processors are mounted.

⚠️ Reaching Millikelvin Temperatures Is About More Than Cooling

At these temperatures, even tiny heat loads become significant.

Researchers must carefully manage:

❄️ Thermal radiation from warmer stages
⚡ Joule heating in electrical wiring
📡 Radio-frequency and microwave noise
🔧 Mechanical vibrations from cryocoolers
🌬️ Residual gas conduction in imperfect vacuums

A single poorly filtered cable or an insufficient thermal anchor can raise the sample temperature by several millikelvin.

17/06/2026

📢 New Publication from Our Research Group! 🎉

We are excited to share our latest research in APL electronics devices titled as

“Nanoscale Cathodoluminescence Probing of Neutral and Charged Excitons with Tunable Photo-Capacitance in RIE-Thinned WSe₂.”

In this work, we explore the fascinating excitonic behavior in RIE-thinned WSe₂ using high-resolution cathodoluminescence spectroscopy combined with photo-capacitance measurements. By probing both neutral and charged excitons at the nanoscale, our study provides new insights into the optoelectronic properties of two-dimensional semiconductors and demonstrates tunable photo-capacitance, opening avenues for next-generation nano-optoelectronic and quantum devices.

We congratulate all the authors and collaborators for this achievement and look forward to further advancing research in 2D materials and nanoscale characterization.



DOI:

This study presents the thickness-dependent excitonic physics of WSe2 achieved through a precisely controlled reactive ion etching (RIE) process, enabling deter

14/06/2026

Cryogenic week's Fifth Post: The Strange World Near Absolute Zero

As temperatures approach absolute zero, something extraordinary happens.

The familiar world around us begins to disappear, and a hidden quantum world emerges.

At room temperature, atoms and electrons are constantly jiggling due to thermal energy. Their random motion masks many fascinating quantum effects.

But as we cool matter to cryogenic temperatures, thermal motion fades away, allowing nature to reveal some of its deepest secrets.

⚡ Superconductivity: Electricity Without Resistance

Normally, electrons lose energy as they move through a material, producing heat.

However, below a critical temperature, certain materials undergo a dramatic transformation and become superconductors, carrying electrical current with zero resistance.

This remarkable phenomenon powers:
🩺 MRI scanners
🔬 Particle accelerators
⚛ Quantum computers
⚡ Future fusion reactors

Imagine transmitting electricity across an entire country without losing any energy—that's the promise of superconductivity.

🌊 Superfluidity: A Liquid That Defies Intuition

When helium is cooled below about 2.17 K, it enters a bizarre state known as a superfluid.

Unlike ordinary liquids, superfluid helium has essentially zero viscosity.

It can:
💧 Flow through microscopic channels
🌀 Climb the walls of its container
🔄 Continue circulating for extraordinarily long times without slowing down

It behaves more like a macroscopic quantum wave than a conventional liquid.

🌌 Bose-Einstein Condensation: Atoms Acting as One

At ultralow temperatures, certain atoms can lose their individual identities and merge into a single quantum state known as a Bose-Einstein Condensate (BEC).

Instead of billions of independent particles, the entire cloud behaves like one giant matter wave.

BECs provide a unique window into quantum mechanics and have enabled precision measurements, atom interferometry, and studies of exotic quantum phases.

🧲 Quantum Materials & Spintronics

Cryogenic temperatures are invaluable for exploring the magnetic and electronic properties of advanced materials.

Researchers use low temperatures to study:

🧲 Spin transport over long distances
🧲 Spin-orbit interactions and spin Hall effects
🧲 Magnetic skyrmions and topological spin textures
🧲 Superconducting spintronics
🧲 Novel quantum materials and correlated electron systems

By suppressing thermal fluctuations, cryogenics allows subtle quantum effects to be observed with much greater clarity, guiding the development of future low-power electronic and spin-based technologies.

📸 Detecting a Single Photon

At cryogenic temperatures, detectors become so sensitive that they can register the arrival of a "single photon".

Superconducting nanowire single-photon detectors (SNSPDs) are enabling breakthroughs in:

✨ Quantum communication
🔐 Quantum cryptography
🌌 Astronomy
📡 Deep-space optical links
💻 Quantum computing

🤔 Does Everything Stop at Absolute Zero?

Surprisingly, no.

Even as temperature approaches 0 K, quantum mechanics prevents particles from becoming perfectly motionless.

Due to the "Heisenberg uncertainty principle", atoms retain a tiny amount of unavoidable zero-point motion.

🚀 Cryogenics is far more than a way of making things cold.

It is a gateway to a hidden world where electricity flows without loss, liquids climb walls, atoms behave as a single entity, and quantum effects dominate reality.

The closer we get to absolute zero, the stranger—and more fascinating—the universe becomes.

04/06/2026

Cryogenic week: The fourth post - The Race to Absolute Zero: One of Humanity's Greatest Scientific Adventures

Today, we take refrigerators, air conditioners, and liquid nitrogen for granted. But less than 200 years ago, scientists weren't even sure whether there was a limit to how cold something could become.

The quest to reach lower and lower temperatures became one of the most ambitious scientific races in history—a race that transformed our understanding of matter, energy, and the quantum world.

🌡️ The Beginning: When Cold Was a Mystery

In the early 1800s, many scientists believed that certain gases such as oxygen, nitrogen, and hydrogen could never be liquefied. They were called *"permanent gases"* because no one had ever succeeded in turning them into liquids.

Then came a series of breakthroughs.

Researchers discovered that by applying enormous pressure and carefully removing heat, even these "permanent" gases could be liquefied.

What seemed impossible suddenly became achievable.

🔹 Oxygen was liquefied.
🔹 Nitrogen was liquefied.
🔹 Hydrogen was liquefied.

Each success pushed humanity closer to absolute zero.

But one gas refused to surrender:

Helium (He) or element 2.

🧊 The Helium Challenge

Helium was the final boss of cryogenics.Unlike other gases, helium remains liquid at incredibly low temperatures and refuses to solidify under normal pressure.

For years, scientists around the world tried and failed to liquefy it.

Then, in 1908, Dutch physicist "Heike Kamerlingh Onnes" succeeded in producing liquid helium at 4.2 K.

At that moment, humanity entered a temperature regime never before explored.

⚡ A Discovery That Changed the World

Onnes wasn't trying to revolutionize technology. He simply wanted to measure how electrical resistance behaves at very low temperatures. But in 1911, he observed something astonishing.

The electrical resistance of mercury suddenly vanished.

Not decreased, Not became small, It "completely" disappeared.

The world had just discovered superconductivity.

Today, that discovery powers:

🧲 MRI scanners
⚛ Particle accelerators
🚄 Maglev transportation
⚡ Future fusion reactors
💻 Quantum computers

One of the most important technologies of the modern world was discovered simply because someone managed to make a material cold enough.

🌊 The Colder We Went, The Stranger Nature Became

Scientists expected matter to become quieter and simpler at low temperatures. Instead, it became more mysterious.

At cryogenic temperatures researchers discovered:

✨ Superconductivity – electricity flowing without resistance
✨ Superfluidity – liquids flowing without viscosity
✨ Quantum tunneling on macroscopic scales
✨ Bose-Einstein condensation
✨ Exotic quantum states of matter

🤯 The Surprising Truth About Absolute Zero

Most people imagine that cooling something is simply a matter of removing heat. But nature becomes increasingly stubborn as temperature decreases.

Going from: 300 K → 77 K is relatively straightforward.

Going from: 1 K → 0.01 K can require:

❄ Ultra-high vacuum systems
❄ Sophisticated cryogenic refrigeration
❄ Radiation shielding
❄ Vibration isolation
❄ Extraordinary engineering precision

Each step becomes harder than the last.

🚀 The Race Continues

Today, scientists routinely reach temperatures below one millikelvin—less than one-thousandth of a degree above absolute zero.

These ultra-cold environments are enabling breakthroughs in:

⚛ Quantum computing
🧲 Superconducting electronics
📸 Single-photon detectors
🔄 Spintronics and quantum materials
🌌 Precision measurements of the universe

Yet one challenge remains.

According to the laws of thermodynamics, "absolute zero itself can never be reached."

No matter how advanced our technology becomes, there will always be a tiny amount of residual motion because according to the Third Law of Thermodynamics, absolute zero can never be reached through any finite cooling process. As matter approaches 0 K, removing the remaining thermal energy becomes increasingly difficult. Moreover, quantum mechanics tells us that particles can never be perfectly at rest. Due to the Heisenberg uncertainty principle, they retain a small amount of unavoidable zero-point motion. The closer we get to absolute zero, the harder nature pushes back.

The finish line is forever out of reach. And perhaps that is what makes the race so fascinating.

🌡️ Humanity's journey toward absolute zero is not merely a story about temperature—it's a story about curiosity, persistence, and the discovery of entirely new worlds hidden within the cold.

01/06/2026

Cryogenics week: The third post

❄️ Why Do We Need Cryogenics?❄️

In our previous posts, we explored what cryogenics is and how scientists cool systems from room temperature all the way down to mili kelvin.

But a natural question arises:

Why do we invest so much effort in reaching such extreme temperatures?

The answer lies in a remarkable fact:

Many of the most advanced technologies known to humanity either rely on cryogenics or were discovered because of it.

1. Microelectronics & Semiconductor Research

Modern electronics is approaching fundamental physical limits, such as, on its gate length. Cryogenic environments allow researchers to investigate,

⚡ Carrier transport mechanisms
⚡ Noise and reliability in electronic devices
⚡ Advanced transistor architectures
⚡ Low-power and high-performance computing technologies

This helps researchers understand how materials and devices behave when thermal effects are minimized.

2. Spintronics

One of the most exciting frontiers of modern electronics is spintronics, where information is processed not only through the electron's charge but also through its spin. Cryogenic systems enable researchers to:

🧲 Investigate spin transport over long distances such as magnonics
🧲 Study the origins of the spin related effects like spin Hall effect
🧲 Explore magnetic skyrmions and topological spin textures
🧲 Probe ultrafast magnetization dynamics
🧲 Develop low-power memory and logic technologies
🧲 Study quantum systems such as NV centers and spin qubits

3. Advanced Sensors & Detectors

Cryogenic detectors are among the most sensitive measurement devices ever built. At cryogenic temperature small amount of energy can be detected with remarkable precision. They are used in:

📸 Single-photon detectors (SNSPDs and TES)
🔬 Dark matter searches
🌌 Cosmic microwave background experiments
📡 Radio astronomy
⚛ Quantum sensing and metrology

4. Quantum Computing & Quantum Technologies

⚛ Quantum coherence can be preserved for longer durations
⚛ Quantum states become more stable and controllable
⚛ Decoherence and thermal noise are drastically reduced

5. MRI & Medical Imaging

Modern MRI scanners rely on superconducting magnets capable of generating extremely strong magnetic fields with minimal power loss. These magnets must be cooled to cryogenic temperatures to operate reliably.

6. Particle Accelerators

The Large Hadron Collider (LHC) at CERN uses thousands of superconducting magnets operating near 1.9 K—colder than outer space—to guide particle beams traveling close to the speed of light.

7. Space Science & Astronomy

Infrared telescopes, space observatories, and astronomical detectors are often cooled cryogenically to suppress thermal noise and reveal faint signals from distant stars, galaxies, and exoplanets.

8. Fusion Energy

Future fusion reactors use massive superconducting magnets to confine plasma at temperatures exceeding millions of degrees. Ironically, some of the hottest systems ever created by humans depend on some of the coldest technologies.

9. Fundamental Physics

Cryogenics has enabled the discovery of some of the most fascinating phenomena in modern physics:

✨ Superconductivity
✨ Superfluidity
✨ Bose-Einstein Condensation
✨ Quantum phase transitions

The remarkable thing about cryogenics is that it often remains invisible to the public. Yet it quietly powers breakthroughs in electronics, computing, medicine, energy, astronomy, materials science, and fundamental physics.

31/05/2026

Cryogenics week : The second post

Q) How Do We Reach Temperatures Close to Absolute Zero?

In our previous post, we explored how cryogenics has evolved and why achieving lower temperatures is increasingly difficult. But a fascinating question remains:

How do scientists actually create such extreme cold?

The answer is: there isn't a single method. Different temperature ranges require entirely different cooling technologies.

🔹 300 K → 77 K
Liquid nitrogen is often the first step. At 77 K (-196°C), it provides an inexpensive and efficient gateway into the cryogenic world.

🔹 77 K → 4.2 K
To go further, we enter the realm of liquid helium. Helium remains liquid down to 4.2 K, enabling superconducting magnets, MRI systems, and many low-temperature physics experiments.

🔹 4.2 K → Below 1 K
Now things become much more challenging. Techniques such as pumped helium systems and helium-3 refrigeration are used to remove the remaining thermal energy.

🔹 Below 100 mK
At these temperatures, conventional cooling is no longer sufficient. Scientists use dilution refrigerators that exploit quantum properties of helium-3 and helium-4 mixtures to continuously remove heat.

🔹 Towards Absolute Zero
Reaching temperatures of just a few millikelvin requires extraordinary engineering:
❄ Ultra-high vacuum systems
❄ Multiple radiation shields
❄ Vibration isolation
❄ Specialized wiring and filtering

Today, these ultra-low temperatures enable breakthroughs in:
⚛ Quantum computing
🧲 Superconductivity research
🔬 Quantum materials
🚀 Space instrumentation
📡 Ultra-sensitive detectors

As we approach absolute zero, we are not just making things colder—we are entering entirely new regimes of physics where matter behaves in ways impossible to observe at ordinary temperatures.

🌡️ The colder we go, the stranger and more fascinating the universe becomes.

❄Stay tuned for the updates❄

30/05/2026

Cryogenic week : The first post

In this series, we would like to bring the science of cryogenics.

🌡️ Everything in Cryogenics Starts with One Fundamental Quantity: Temperature

Temperature is one of the most basic concepts in physics, yet pushing it lower and lower has unlocked some of humanity's most remarkable technological achievements.

The journey began in the 19th century when scientists first learned how to liquefy gases. What started as a scientific curiosity evolved into a field that now enables MRI scanners, particle accelerators, space exploration, superconducting magnets, and even quantum computers.

As we move down the temperature scale, the challenges grow dramatically:

🔹 Room Temperature (~300 K) – Everyday world
🔹 Liquid Nitrogen (77 K) – The gateway to cryogenics
🔹 Liquid Helium (4.2 K) – Where superconductivity becomes commonplace
🔹 Millikelvin Regime (

13/04/2026

Heartiest congratulations to Dr. Prabal Dweep Kanikar on the successful defense of his PhD! 🎓✨

This remarkable achievement is a testament to your dedication, perseverance, and passion for research. It has been a privilege to witness your hard work and commitment throughout this journey.

Thank you for your contributions, efforts, and the inspiration you bring to those around you. Wishing you continued success, new opportunities, and many more accomplishments in the future ahead.

Best wishes from CARE family for an exciting and impactful journey forward!

IIT Delhi

07/04/2026

🚀 Radiation-Resilient RF Electronics

Proud to highlight a publication from our research team in IEEE Transactions:

“Effect of Gamma Radiation on Static DC, Reliability, and RF Performance of Submicron GaN-on-Si RF MIS-HEMTs With In Situ SiN.”

This work examines the impact of gamma radiation on GaN-based RF devices, addressing performance and reliability in extreme environments such as space and nuclear systems.

🔗 Read the paper: https://doi.org/10.1109/TDMR.2025.3573183

👏 Congratulations to the team on this achievement.

This work demonstrates the synergistic effects of 100 kGy gamma irradiation on the electrical and reliability performance of submicron GaN-on-Si RF MIS-HEMTs wi

30/03/2026

Excited to share Faculty Spotlight video on the IIT Delhi YouTube channel—get an inspiring glimpse into groundbreaking research and insights from our esteemed faculty,
Prof. Rahul Mishra
IIT Delhi

This will be the discription - What if the next leap in wireless technology could unlock ultra-high-speed communication, advanced sensing, and the future of...