Hold the rotor with your eyes

1 · Find what holds the rotor

Beginner

Once the rotor is released, what localises its state?

A laser trap that keeps pulling it back to the centre The suspension fibre, which pulls it back every 15 seconds The continuous measurement of its angle

2 · Work out the reference time

Continuous measurement sets a reference angular frequency Ω_ref = 2π × 6 Hz. The reference time, the time the conditioned state takes to settle, is t_ref = 1/Ω_ref.

Intermediate

What is t_ref?

About 167 ms About 26 ms About 2.6 ms

3 · Explain the unreachable zero

For this level of isolation, the model predicts a minimum entropic temperature of about 15 nanokelvin, however much the position measurement is improved.

Expert

Why can it not go down to zero?

A free object has no natural frequency, so no real temperature Measuring position more finely blurs the rotation more The measuring laser always keeps it above one microkelvin

4 · Compare the two estimates

On the same 100 stretches of 1.25 seconds, the causal estimate gives 1.2 microkelvin and the smoothed estimate 140 nanokelvin.

Expert

Where does the difference come from?

Smoothing also uses the measurements made after the instant studied Smoothing really cools the rotor, using the push beam The two estimates come from different experiments, in different vacuums

Rotor held

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