# Tag Info

### In real life, for a tennis ball to go through a wall, does it have to completely prevent the particles from interacting? (decoherence)

The problem is the tension here between "real life" and "infinitely". In "real life" we cannot do an experiment infinitely many times, and if we tried other factors like ...
• 28.1k
Accepted

### What is the meaning of this statement in Optics, Born-&-Wolf regarding coherence length?

... by supposing that the light of the spectral line is not strictly monochromatic, but is made of wavetrains of finite length ... What the authors mean is this. The wave actually is not an ideal ...
• 28.2k
Accepted

### What does "coherent evolution" of an $N$-body quantum system mean?

Schrödinger equation for N-body system A system evolves coherently, if there are no dephasing/decoherence effects, i.e., its evolution can be simply described by its Hamiltonian and the Schrödinger ...
• 42.3k
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### What does the coherence time signifies?

Coherence time ($\tau$) is a measure of the correlation between phases of a wave at two different instances of time. It essentially tells you if a traveling beam remains 'in-phase' with itself after a ...
1 vote
Accepted

### What is the difference between coherence and entanglement?

Coherence means particular type of correlation (of phase; say) between two points on a wavefront or etc (see optics by Hecht); here two points "does not" reside in space-like separation [of ...
• 36
1 vote
Accepted

### Is this an example of a spatially coherent wave?

Spatial coherence is usually described in terms of a coherence length. This is the distance over which a fixed relationship is maintained. Where fixed means the difference is small enough to ignore ...
• 28.2k
1 vote
Accepted

### How does lasers emit photons of constant phase and frequency

The source of the photons that coming out from the laser is due to a process called stimulated emission, you are right that all the photons doesn't have excatly the same frequency, this is called ...
• 459
1 vote

### Will quantum events ever occur on a macro-scale rather than a vacuum? Michio kaku says there's a chance we'll wake up on Mars tomorrow

The rate of a tunneling event in which an object of your mass (or any human's mass) moves from Earth to Mars is not zero, but so small that by the time it has a reasonable chance to occur, you, Mars, ...
• 36.1k
1 vote

### Will quantum events ever occur on a macro-scale rather than a vacuum? Michio kaku says there's a chance we'll wake up on Mars tomorrow

Waking up on Mars is impossible for any reasonable interpretation of impossible. However, macro-scale events that are prohibited in classical physics but predicted by QM, in environments far from ...
• 9,825
1 vote
Accepted

### Why aren't macroscopic objects—or really the entire universe—coherent?

The comment thread looks a bit like it's going in circles so I will just make the bold claim. To the best of our knowledge, macroscopic objects, including the entire universe, are coherent. The reason ...
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### Coherence and superposition principle - equivalent properties?

Imagine a generic pure state$^\dagger$, which is a superposition of some basis states $$|\Psi\rangle = \sum_{k=1}^N c_k | k \rangle$$ To be concrete, we can take the basis ...
• 36.1k
1 vote

### Long temporal coherence sunlight

From this presentation: . Temporal Coherence is a measure of the correlation of light wave’s phase at different points along the direction of propagation – it tells us how monochromatic a source is. ...
• 224k
1 vote

### Gaining Quantum information without destroying the coherence

Consider you have telescope (T1) and you observe a spec of light which you know to be 2 stars ... but your telescope just can't resolve it. With some study you realize you are diffraction limited (...
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1 vote

### Degree of first-order coherence doesn't imply always 100% visibility?

The issue seems to be about the definition of coherence. The OP states that multimode light could be perfectly coherent. In the context of temporal coherence the term multimode means multiple ...
• 12.5k
1 vote

### Do stars produce spatially coherent light? Why?

Starlight is not coherent in the sense that all Photons at a given frequency arrive in the same phase. Starlight is incoherent in phase but because of the distance to the source it acts as a point ...

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