This article explores fundamental concepts of quantum physics such as superposition, uncertainty principle, and entanglement through experiments and quantum programming. It discusses how quantum mechanics challenges our classical understanding of reality, illustrated by phenomena like Schrödinger's cat paradox and quantum teleportation, highlighting the profound implications for science and technology.
Quantum physics, a field that emerged in the early 20th century, challenges our classical understanding of reality. This article delves into some of the most intriguing quantum phenomena, illustrating them through experiments and quantum programming. We explore concepts such as superposition, the uncertainty principle, entanglement, and their implications for the nature of reality.
Quantum physics asks one of the deepest questions humanity can pose: What is the true meaning of reality? Although the subject may not offer immediately practical knowledge for software developers, it provides profound insights into the fabric of the universe.
We will examine several quantum experiments and reconstruct them using a quantum programming language called Q. This approach leverages the software developer's skill in modeling and reasoning about complex systems.
Quantum physics began in 1900 when Max Planck introduced the concept of energy quanta to solve the black body radiation problem. He proposed that energy is not continuous but comes in discrete packets, now known as quanta, characterized by the Planck constant — an incredibly small number.
For about 25 years, physicists struggled to model the atom using classical mechanics, which treated the atom like a miniature solar system. This model was unstable and collapsed mathematically.
The breakthrough came in 1925 when Werner Heisenberg introduced quantum mechanics, focusing on observables — quantities that can be measured. Quantum mechanics became one of the most successful scientific theories, underpinning modern technology such as transistors, semiconductors, GPS, MRI scanners, and more.
However, quantum mechanics does not provide an objective description of reality but rather a mathematical toolbox that predicts measurement outcomes. This leads to various interpretations and philosophical questions about the nature of reality.
A beam splitter is a device that splits a beam of light into two beams. Light behaves both as a wave and as particles called photons. When a single photon is sent through a beam splitter, it randomly ends up at one of two detectors with equal probability.
Using the quantum programming language Q, we can model a photon as a quantum bit (qubit). Applying the Hadamard (H) transformation simulates the beam splitter, and measuring the qubit corresponds to detecting the photon. Running this simulation multiple times yields roughly equal detections at both detectors.
Stacking two beam splitters with mirrors creates the Mach-Zehnder interferometer. Classical wave interference explains why photons always exit through one detector in this setup.
However, when sending single photons, quantum mechanics reveals that the photon exists in a superposition of both paths simultaneously, interfering with itself. This explains the observed detector outcomes but challenges classical intuition.
Introducing detectors along the paths to observe the photon collapses the superposition, causing the interference pattern to disappear. The photon then behaves as if it randomly chooses a path, demonstrating that observation affects the system.
Erwin Schrödinger illustrated superposition with a thought experiment involving a radioactive atom, a poison release mechanism, and a cat in a box. The atom's decay is a quantum event in superposition of decayed and not decayed states. Consequently, the cat is simultaneously dead and alive until observed.
In Q, the atom is modeled as a qubit in superposition with a 90% chance of no decay and 10% chance of decay. The cat is represented by two qubits entangled with the atom. Measurement collapses the system to either the cat alive or dead state.
Large objects like cats cannot maintain superposition due to interactions with the environment (decoherence). Experiments have created superpositions of thousands of atoms for milliseconds, but macroscopic superpositions are practically impossible.
Spin is a quantum property analogous to angular momentum with components along x, y, and z axes. Each component can have values +1 or -1 (up/down).
The Stern-Gerlach apparatus measures spin by deflecting electrons in a magnetic field. Measuring spin along one axis yields definite results, but measuring along a perpendicular axis yields random outcomes.
An electron qubit initialized with spin up along z measured along z yields deterministic results. Measuring along x yields random results, illustrating the uncertainty principle.
Measuring spin along x and then z axes in sequence shows that the second measurement becomes random, indicating loss of information due to incompatible observables.
Formulated in 1927, it states that certain pairs of physical properties, like position and momentum or spin components, cannot be simultaneously known with arbitrary precision. This principle is fundamental to quantum mechanics and underlies quantum cryptography.
Due to the uncertainty relation between energy and time, empty space is not truly empty but exhibits quantum fluctuations where virtual particles appear and annihilate rapidly. These fluctuations have measurable effects, such as the Casimir effect.
Entanglement occurs when two quantum particles become linked such that the state of one instantly influences the state of the other, regardless of distance.
Two entangled electrons are sent to distant detectors. Measurements show perfectly correlated results even when separated by kilometers and measured simultaneously, precluding communication faster than light.
Two qubits are entangled using the controlled NOT (CNOT) operation after placing one in superposition. Measuring both in the same basis yields perfectly correlated results.
Einstein proposed hidden variables (pre-agreed instructions) to explain correlations, calling entanglement "spooky action at a distance." Quantum mechanics predicts stronger correlations than any classical hidden variable theory.
John Bell formulated a theorem in the 1960s that allowed experimental tests distinguishing these explanations. Experiments by Aspect, Clauser, and Zeilinger confirmed quantum mechanics' predictions, disproving local hidden variables.
Entangled states cannot be decomposed into individual states of particles, existing only as a combined system. This non-locality challenges classical notions of reality.
Using entanglement, quantum teleportation transfers the state of a qubit from one location to another without moving the particle itself.
Alice and Bob share an entangled pair of qubits. Alice entangles the qubit to be teleported with her half of the pair and measures them, sending the classical measurement results to Bob. Bob applies corresponding transformations to his qubit, recreating the original state.
No information travels faster than light since classical communication is required. The original qubit state is destroyed during measurement, ensuring no cloning occurs.
Quantum teleportation has applications in quantum communication and cryptography.
Quantum physics reveals a reality that defies classical intuition, where particles exist in superpositions, measurement affects outcomes, and entangled particles exhibit instantaneous correlations. These phenomena have profound implications for technology, philosophy, and our understanding of the universe.
For software developers, modeling these quantum experiments in code offers a unique perspective on quantum mechanics, bridging abstract theory and practical simulation.
If you are intrigued by these topics, exploring quantum programming and the philosophy of quantum mechanics can be a rewarding journey into the fundamental nature of reality.
This article was inspired by a presentation at NDC London 2026 by Filip W., who demonstrated quantum physics concepts through programming and experiments.
