Marisol sends one photon at the two slits and does not measure which slit it uses. No detector watches the slits. What is the photon's path condition while nobody measures it?
A quantum object can be in different quantum states, like the two slit paths. This lesson says what quantum physics found about an unmeasured object, and it names that condition with a word you met once before, doing a different job.
While no measurement is made, a quantum object can be in several of its quantum states at once.
Marisol's unmeasured photon is not secretly on one path. It is in both slit-path states at once.
A measurement changes the situation. When a measurement is made, a single definite outcome appears: one path, one position, one energy.
If a detector measures which slit the photon used, the answer is one slit, every time. The superposition is a before-measurement condition.
In the waves topic you met superposition with a different meaning: two overlapping waves add their displacements.
Quantum superposition is a different idea that shares the name. No displacements add here. A quantum superposition is one object in several of its own states at once, until a measurement is made.
How the one outcome gets picked is a question this course leaves open. The tested statement is the one above: several states at once, and a single definite outcome when a measurement is made.
Kenji's electron, unmeasured, could be at a low energy or at a high energy. A measurement of its energy is then made. Describe the electron's condition before and after the measurement.
Before the measurement, the electron is in a superposition: both energy states at once.
The measurement makes a single definite outcome appear: one energy, low or high.
After the measurement, the electron's energy condition is one definite state.
Before: a superposition of the two energy states. After: one definite energy.
A student says a photon in a superposition of two paths is the same as two water waves adding their heights. What is the difference?
Two water waves adding is the waves topic's superposition: two separate waves overlap, and their displacements add.
A quantum superposition is one object in several of its own states at once.
Nothing adds its displacement to anything here, and there is only one object.
They share a name and nothing else: wave superposition adds two waves' displacements, and quantum superposition is one object in several states at once.
Marisol's photon is in a superposition of two path states. A detector then measures its path. What does the detector find?
Kenji says: 'A photon in a superposition of both slit paths is just like two overlapping waves adding their displacements.' Is Kenji correct?
Jocasta says: 'A quantum object can be in several quantum states at once, and a single definite outcome appears only when a measurement is made.' Is Jocasta correct?
Which statement says what a quantum superposition is?
An unmeasured electron is in a superposition of a low energy and a high energy. Its energy is then measured. What does the measurement give?
The word 'superposition' does two different jobs in this course. Which statement gives the quantum meaning?