RajeshKumarKrishnan
I build quantum communication systems and quantum sensing products, and I write books that explain the physics behind them.
Senior VP – Innovation, QNu Labs, Bengaluru
PhD candidate, Eindhoven University of Technology
0photons detected. Each dot is one photon sent through two slits. The fringes appear only after thousands have arrived.
From the lab bench to quantum products in the field
What I work on
Quantum communication and quantum sensing, from the laser pulse and the atomic vapour cell to a product that works in the field.
Research and patents
Peer-reviewed work and patent filings with colleagues at QNu Labs and TU/e, from photon sources to network protocols.
Journal and conference papers listed
Patents listed
Quantum Lab
Five experiments to play with
Test how strong your password really is, catch an eavesdropper, break a reused one-time pad, sense a magnetic field with atoms, and check whether your data is safe from future quantum computers.
How strong is your key?
Strength is measured in bits: each bit doubles the number of guesses an attacker needs. Common words, names, years and keyboard patterns are guessed first, so they add almost nothing.
A future quantum computer running Grover's algorithm needs only about the square root of the guesses, which halves the effective bits. That is why quantum-safe systems use 256-bit keys, and why the keys themselves should come from true randomness.
kept, bits agreekept, bits disagreebases differ, thrown away
Catch the eavesdropper
Alice encodes each bit in one of two bases, straight (+) or diagonal (×). Bob measures in a random basis. They keep only bits where the bases matched. An eavesdropper must also guess bases, and her wrong guesses disturb about a quarter of the kept bits.
Challenge. Turn Eve on and lower how many photons she intercepts. Can she learn a useful share of the key while staying under the 11% alarm?
Send some photons.
00Break a reused key
A one-time pad, a random key XOR-ed with the message, is perfectly secure. Quantum key distribution exists to deliver such keys. But the pad must never be used twice.
Reuse it, and XOR-ing the two ciphertexts cancels the key completely: \(C_1 \oplus C_2 = M_1 \oplus M_2\). An attacker then slides a guessed word along the result. Wherever the guess is right, readable text from the other message appears.
Generate a key to encrypt message 1.
Sense a field with atoms
An optically pumped magnetometer uses a laser to line up the spins of caesium atoms in a small glass cell. Released, the spins precess around the magnetic field like tiny gyroscopes, and a probe beam reads out their fading signal.
The precession frequency is fixed by nature: about 3.5 Hz for every nanotesla of field. Measure the frequency and you have measured the field, with a precision that lets a drone map objects buried under the ground.
Caesium ground state, gyromagnetic ratio about 3.50 Hz/nT. The precession on screen is slowed down by a factor of many thousands so the eye can follow it.
Quantum threat clock
Mosca's inequality: if the years your data must stay secret (\(x\)) plus the years you need to migrate to quantum-safe cryptography (\(y\)) exceed the years until a cryptographically relevant quantum computer (\(z\)), data encrypted today can be recorded now and decrypted later.
Books
Physics written the way I wish I had been taught it, every step shown and every idea given a picture.
Talks and teaching
Writing
Technical notes on the problems I work on: photons, detectors, keys, randomness and post-quantum hardware.