The Qubit Thought Experiment
In order to truly understand the basis of quantum physics and quantum technologies, one needs to comprehend the paradigm that is the quantum bit or qubit. As a business guy, I traditionally stay at the practical level of any new technology (how can it impact ROI, KPI’s etc.) but digging deeper, for those kindred curious spirits, it can be very enlightening to delve a few layers down.
Try this thought experiment.
You hold a qubit in your hand. (It could be ytterbium, rubidium, neural atom or some other form of qubit). You expose it to a number of different environmental changes and see what happens. First you shake it. Next you heat it up. Next you cool it down. Next you expose it to radiation. Finally you expose it to time. Let’s see what happens in each case.
Image source: Brian Lenahan/Midjourney
Imagine an individual holding this quantum bit (qubit) in their hand, like a delicate bead of information suspended in a superposition of 0 and 1. This qubit isn't just an abstract concept; in this experiment, it is made manifest as a small particle, embodying the fragile and enigmatic nature of quantum states.
Phase 1: Initial State - The Pristine Qubit
In the individual’s hand, the qubit exists in a state of perfect superposition, a delicate balance between 0 and 1, held in a perfectly isolated environment. The individual observes the qubit through specialized goggles that allow them to perceive its superposition as a swirling, multicolored sphere of potential outcomes. At this moment, the qubit's state is untangled, unperturbed by the outside world.
Phase 2: Movement - The Chaotic Dance
The individual begins to move, walking and swaying their hand. This introduces slight vibrations, creating a mechanical disturbance. The qubit, once perfectly isolated, now feels the jittering of space and position. The individual notices the qubit flicker; its superposition begins to wobble.
Thought Question: To what degree does physical movement disturb the coherence of a quantum state?
Phase 3: Heat - Thermal Excitement
Next, the individual walks into a warm environment, raising the temperature surrounding the qubit. The once pristine quantum state begins to interact with the thermal energy, causing random fluctuations as the heat excites the particles around it. The superposition becomes blurry, and the individual can barely make out its distinct state.
Thought Question: How does heat-induced noise degrade the delicate coherence of a qubit? At what point does it lose its quantum properties entirely and become a classical state?
Phase 4: Cooling - Freezing Isolation
The individual then moves into a cold chamber where the temperature plummets near absolute zero. The thermal noise is now nearly nonexistent. The qubit, which had almost collapsed due to heat, begins to stabilize once more, approaching a nearly perfect superposition again. The sphere in their hand glows dimly, but it retains its duality.
Thought Question: How does cooling aid in restoring coherence? Can freezing environments fully repair the damage caused by previous interactions with heat?
Phase 5: Radiation - Entangling with the Universe
The individual exposes the qubit to an electromagnetic field, bombarding it with radiation. Photons from the radiation field interact with the qubit, potentially causing quantum entanglement or measurement. The individual now sees the qubit splitting, fragmenting into several smaller, tangled spheres that no longer exist as a pure state.
Thought Question: How does exposure to radiation disturb quantum states, and can radiation cause spontaneous measurement or collapse of the superposition?
Phase 6: Time - The Decay of Information
Finally, the individual waits, holding the qubit over time. Without external interference, the qubit begins to naturally lose coherence due to quantum decoherence, where its environment continuously interacts with it at a microscopic level. Over time, the qubit evolves into a classical state as the delicate quantum superposition decays irreversibly.
Thought Question: How does time alone, through gradual entanglement with the environment, lead to the eventual collapse of quantum information into classical certainty?
Summary
As any quantum physicist worth their salt would I have taken some serious artistic license to draw out this thought experiment, but for those non-physicists graphic or visual impressions are always a wondrous starting point.
Through these environmental changes—movement, heat, cooling, radiation, and time—the individual witnesses the fragility of the quantum world. The qubit's journey from perfect superposition to classical collapse is a vivid reminder of how interconnected quantum systems are with their environment, unable to maintain their mysterious states in the face of macroscopic forces.This thought experiment raises profound questions about the preservation of quantum information, the impact of environmental "noise," and the ultimate fate of quantum states in the macroscopic world we live in.
Brian Lenahan is founder and chair of the Quantum Strategy Institute, author of seven Amazon published books on quantum technologies and artificial intelligence. Brian’s focus on the practical side of technology ensures you will get the guidance and inspiration you need to gain value from quantum now and into the future. Brian does not purport to be an expert in each field or subfield for which he provides science communication.
Brian’s books are available on Amazon. Quantum Strategy for Business course is available on the QURECA platform.
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