process

feedback

Using information from a measurement to adjust a system's parameters, enabling energy extraction in quantum protocols.
86 related articles

Description

Feedback in quantum physics is the process of using the outcome of a measurement to adjust the parameters of a quantum system in real time. Unlike classical feedback, which simply corrects errors, quantum feedback can be used to actively steer a system into desired states, extract energy from it, or protect it from decoherence. This is central to many quantum technologies, from error correction in quantum computers to the operation of quantum batteries and sensors.

History

The concept of feedback control in quantum systems was formalized in the 1980s–1990s, with key contributions by H. M. Wiseman and G. J. Milburn, who developed the theory of quantum feedback control.

How it works

A measurement on a quantum system yields a probabilistic outcome. The result is fed back to a controller, which applies a specific operation (e.g., a laser pulse or a magnetic field change) to the system. Because the measurement itself disturbs the quantum state, the feedback must be designed to account for this back-action. In energy extraction, for example, a measurement can reveal the system's state, and a subsequent operation can be tuned to extract work from it, effectively using information as a resource.

In practice

Used in quantum error correction, quantum metrology (e.g., adaptive measurements), and in proposed quantum battery charging protocols.

Fun fact

In the quantum Mpemba effect, feedback can be used to accelerate cooling by measuring and re-adjusting the system, making a hotter system cool faster than a colder one.

Concept graph →

Related articles · 86

Quantum Coherence Microscope: Seeing the Phase of Atoms in a Lattice
In a hall with a thousand spectators, applause blends into a general noise, but if someone falls out of rhythm — a ripple runs through the crowd. The quantum world works similarly: atoms in a trap can behave as a single whole, or they can fall apart into independent individuals.
Quantum Physics2026-08-092 minarXiv:2608.08821express
Quantum Puzzle: How Measurements Assemble Complex States
Imagine a huge puzzle where each piece is a quantum particle. To complete the picture, you don't just fit the pieces together: you need to entangle them in a special way. Usually, this is done by carefully applying operations one after another, like assembling the puzzle strictly by the instructions, row by row.
Quantum Physics2026-08-031 minarXiv:2608.01788express
Quantum Mpemba effect: how hot cools faster than cold
A cup of hot coffee sometimes freezes faster than cold tap water. This paradox, known as the Mpemba effect, has long been considered a curiosity of classical physics. Now its quantum counterpart has helped test and tune quantum processors — devices that may one day power supercomputers.
Quantum Physics2026-07-242 minarXiv:2607.24836express
How to Catch the Heat of Emptiness with a Superconducting Circuit
Empty space is not as empty as it seems. According to quantum theory, the vacuum is filled with particles that constantly pop in and out of existence. In 1976, physicist Bill Unruh showed that if an observer moves with acceleration, this 'quantum soup' turns into a genuinely warm bath for them — the Unruh effect.
eess.SY2026-07-151 minarXiv:2607.14245express
How Entropy Helps Robots Find Paths Faster
A search party combs a foggy field. At first, people spread out wide: a high 'temperature' of search means a great variety of attempts. Upon finding a trace, they close in. But the speed of convergence is critical — narrow the circle too early, and the best find stays aside. The coordinator assesses the spread of searchers and commands when to speed up or slow down.
cs.SE2026-07-112 minarXiv:2607.10347express
Quantum System Confuses Blueprints, but Engineers Don't
Quantum devices are no longer lab curiosities. They are assembled, tuned, and repaired like ordinary hardware — except inside them, it's not just current but intricate tangles of particles that can exist in multiple states at once. Engineers draw schematics, programmers write code, physicists calculate effects.
Quantum Physics2026-07-072 minarXiv:2607.06718express
Quantum Physics2026-07-042 minarXiv:2607.03982express
A Recipe for Quantum Experiments: Don't Forget a Thing
A quantum computer is like a finicky musical instrument: the slightest change in temperature, humidity, or string tuning, and the melody sounds different.
The Quantum Doorway: How a Crowd Changes the Rules of Tunneling
Quantum tunneling — the ability of particles to pass through barriers forbidden by classical physics — powers stars with thermonuclear fusion, ignites primordial nucleosynthesis, and gives us flash memory.
Light Quenches Light: Suppressing Instabilities in Gravitational Wave Detectors
In pursuit of gravitational waves, ripples in spacetime left by black holes and neutron stars, detectors like LIGO pump their arms with light of dazzling intensity.
Quantum Physics2026-06-251 minarXiv:2606.26542express
How Atomic Motion Alters Light
Quantum computers of the future will likely communicate via light. An atom stores information, and a photon carries it across the network. But an atom doesn't hang still: it jitters and oscillates, and this motion can corrupt the signal. Previously, engineers could only calculate for a stationary atom.
Quantum Physics2026-06-021 minarXiv:2606.02986express
General Relativity2026-06-021 minarXiv:2606.04099express
Weak Attraction: How Gravity Spares Quantum Superpositions
A single particle can be in two places at once — that's superposition. But any interaction, like a shout, instantly 'collapses' this uncertainty. It was long thought that even gravity could interfere.
Quantum Physics2026-05-292 minarXiv:2606.00254express
Quantum Dance in a Protective Cocoon
A quantum computer is like an orchestra: each musician plays their own part, but the slightest noise from the audience can throw off the whole ensemble. The particles that store information easily lose their coherence from thermal jolts or stray magnetic fields.
Quantum Physics2026-05-202 minarXiv:2605.20902express
Quantum Physics2026-05-191 minarXiv:2605.19706express
Quantum Droplets: Precision Unattainable
The quantum world is usually drawn with points, but real instruments only see blurry spots. Heisenberg and von Neumann long suspected: precision is unattainable.
Quantum Physics2026-05-191 minarXiv:2605.20180express
Magnetic 'Headphones' for Qubits: A New Way to Fight Quantum Noise
Quantum bits (qubits) are like delicate music in a noisy factory. Ambient magnetic fields constantly 'drown out' their quantum state, turning a coherent signal into cacophony. Usually, this destructive process is slowed by retuning the qubits themselves to different frequencies, but that doesn't always work.
Quantum Physics2026-05-161 minarXiv:2605.16978express
Getting the Most Out of a Weak Signal
Dip your finger into water once, and from that single sensation, try to guess its temperature. In the quantum world, such one-shot measurements happen all the time, except you have to guess invisible parameters: say, the squeezing strength of a laser beam.
Quantum Physics2026-05-152 minarXiv:2605.15784express
Quantum Compression: Measuring a Signal Without Extra Samples
In 1948, engineer Claude Shannon laid the foundations of information theory. The Nyquist–Shannon theorem gave the first answer: to avoid losing a signal, you need at least twice as many measurements as the fastest feature in the signal. In 2006, the method of compressed sensing relaxed this requirement.
Quantum Physics2026-05-152 minarXiv:2605.16559express
A Phase That Knows About Losses
If you carry a cup of coffee slowly and steadily around a room and then return to the same spot, nothing happens to the drink. But in the quantum world, things are different: a particle that makes such a loop comes back not quite the same. It picks up an elusive 'extra'—the geometric phase, which physicists call the Berry phase.
Quantum Physics2026-05-141 minarXiv:2605.14582express
Quantum Batteries: Instant Charging with Squeezed Light
Ordinary batteries lose charge like tea cools down. A quantum battery works differently: its heart is a tiny cavity with darting photons. If you illuminate it with special photon pairs, energy flows into a chain of qubit cells instantaneously — much like a swing gets a boost from strong pushes.
Quantum Physics2026-05-102 minarXiv:2605.09527express
Quantum capacitor charges in an instant
An ordinary battery in a phone stores energy in chemical bonds — slowly, with heat and wear. A quantum capacitor works differently: it charges not with matter but with rhythm. A swing that is pushed in time with its motion accumulates energy in the motion itself, without friction.
Quantum Physics2026-05-092 minarXiv:2605.09014express
Quantum Ripples in a Particle Stream
Throw a stone into a pond, and ripples spread across the water. Throw two stones nearby, and the ripples intersect, creating a pattern of reinforced and canceled waves. That's interference.
Quantum Physics2026-04-302 minarXiv:2604.27648express
A Quantum Translator That Learns from Its Mistakes
A radio picks up a broadcast through crackle and hiss. That's roughly how modern quantum computers work: the useful signal drowns in noise. The longer the computation runs, the more the interference distorts the result.
Quantum Physics2026-04-302 minarXiv:2605.00205express
Quantum and the Cell: Three Roads at the Crossroads
Three craftsmen work in the same workshop. The first tries to figure out whether tiny hourglasses are built into nature's own machinery. The second attaches a laser pointer to a microscope to see details invisible to the naked eye. The third, conversely, takes living threads and carefully weaves them into fragile quantum circuits.
Quantum Physics2026-04-212 minarXiv:2604.18996express
Noise That Doesn't Kill but Disguises
The quantum world is like an orchestra where each musician, a particle, plays their part, and together they create a harmonious symphony. But as soon as noise, random clicks and interference, enters the hall, the melody starts to drift.
Quantum Physics2026-04-192 minarXiv:2604.17518express
A Quantum Battery from Hot Vapor
Steam rising from hot metal is a familiar sight in the kitchen. But if you use rubidium instead of water, that cloud becomes a battery. It doesn't run on chemical reactions but on the quantum coordination of atoms.
General Relativity2026-04-182 minarXiv:2604.18625express
Catching Gravity by the Tail
A stone falls into a pond, and ripples spread in all directions. In much the same way, a massive body creates ripples in spacetime. Only it's not water that oscillates, but the very fabric of reality, and instead of circles, there are gravitational waves.
Quantum Physics2026-04-121 minarXiv:2604.10406express
Birth of Light from the Quantum Void
The quantum vacuum is not emptiness, but a tautly stretched string, where particles constantly appear and vanish. Abruptly changing conditions, like shifting the mirrors of a microcavity, causes the 'string' to emit real photons.
Quantum Physics2026-04-071 minarXiv:2604.05422express
Loss Creates Order: The Quantum Dance of Photons
Two pendulums on a stable table swing independently. If you place them on a shaky surface, vibrations synchronize their motion. The same principle worked on a silicon chip with photons. Scientists created two sources of light that emit pairs of particles.
Quantum Physics2026-03-311 minarXiv:2603.29308express
Noisy Neighbors of Quantum Bits
Quantum computers promise to solve problems that are beyond the reach of ordinary computers. But their components, quantum bits, are very sensitive. One type of quantum bit is an oscillating circuit that can exist in two states, like a pendulum swinging left or right. These states store information.
Quantum Physics2026-03-312 minarXiv:2603.29944express
A Quantum Nose for the Hospital
A modern hospital sensor is like a sensitive microphone in a noisy hall. It picks up a weak signal from the heart or brain, but along with it comes the hum of machines, footsteps, the breathing of neighbors. Separating the desired sound from the interference is a science in itself.
Nuclear Theory2026-03-271 minarXiv:2603.26881express
Nuclear Reactions on a Quantum Computer
When two atomic nuclei collide, the outcome depends on their energy and the angle at which the fragments fly apart. Typically, such calculations demand enormous computing power, and accuracy hits a wall due to approximations.
Quantum Physics2026-03-241 minarXiv:2603.22761express
Quantum Batteries Charge with Explosions in a Time Loop
In quantum batteries, charging can be accelerated by shuffling the steps in time, like a deck of cards. Instead of a smooth energy climb, you get abrupt efficiency explosions, like microscopic supernovae inside atoms.
Quantum Physics2026-03-232 minarXiv:2603.22020express
The Quantum World: Reality as a Cloud of Possibilities
Imagine reality as an undeveloped photograph: until the moment of measurement, it exists only as a cloud of probabilities — a superposition of all possible states. Only the act of observation, like developing film, forces a particle to acquire definite properties.
Quantum Physics2026-03-221 minarXiv:2603.21057express
Quantum Sensor: Noise-Proof Performance
A quantum magnetometer based on hydrogen nuclei works like noise-canceling headphones. It alternately "listens" to the field in two different ways: the noise is the same for both, but the desired signal is different. By subtracting one from the other, the device extracts the signal, reducing interference by more than 1000 times.
Quantum Physics2026-03-211 minarXiv:2603.20612express
Unusual sensors win in noisy labs
In a lab, you measure a very weak signal — say, a tiny change in a magnetic field. The instrument trembles from passing cars, from the experimenter's breathing, from wires heating up. This technical noise can't be fully eliminated, and it sets a limit on precision. An ordinary sensor works like a scale that sways with any draft.
Statistical Mech2026-03-121 minarXiv:2603.11788express
The Quantum Mpemba Paradox: Why Hotter Cools Faster
Hot tea normally takes longer to cool than warm tea, but water sometimes breaks this rule: back in the 1960s, schoolboy Erasto Mpemba noticed that hot ice cream freezes faster than cold. This paradox has moved into the quantum world: a collection of particles can settle down faster if it was initially more excited.
Quantum Physics2026-03-112 minarXiv:2603.10883express
Quantum Physics2026-03-101 minarXiv:2603.11079express
How Charging a Battery Explains Time
Two phones with identical batteries: one charges in a basement with a weak signal, and the process goes slower. The battery percentage here plays the role of a clock hand. Physicists applied the same logic to the quantum world. Their clock is a microscopic battery that stores energy. The charging rate depends on a hidden quantum 'mode'—like a switch.