Related Experiment Video
Updated: Jul 11, 2025
09:23
Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators
Published on: May 30, 2014
14.6K
Quantum noise and its evasion in feedback oscillators
Hudson A Loughlin1, Vivishek Sudhir2,3
1LIGO Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA. hudsonl@mit.edu.
Nature Communications
|November 5, 2023
Summary
The Schawlow-Townes formula, a quantum limit for lasers, universally applies to all feedback oscillators. Quantum noise reduction techniques can achieve sub-Schawlow-Townes linewidths, surpassing standard quantum limits.
Area of Science:
- Quantum Optics
- Physics of Oscillators
- Quantum Information
Background:
- Feedback oscillators, including lasers, are crucial for stable references.
- Their performance is often limited by quantum fluctuations, as described by the Schawlow-Townes formula for lasers.
Purpose of the Study:
- To demonstrate the universal applicability of the Schawlow-Townes formula to all feedback oscillators.
- To identify the sources of quantum noise in feedback oscillator loops.
- To explore quantum strategies for achieving improved oscillator stability.
Main Methods:
- Analysis of quantum noise sources within feedback oscillator loops (amplifier and out-coupler).
- Theoretical framework extending the Schawlow-Townes formula to general feedback oscillators.
- Investigation of quantum phenomena like squeezing and entanglement for noise reduction.
Main Results:
- The Schawlow-Townes formula is shown to be a universal quantum limit for feedback oscillators.
- Quantum noise originates from the amplifier and out-coupler in the feedback loop.
- Squeezing and entanglement enable oscillators with linewidths below the standard quantum limit.
Conclusions:
- The study establishes a general quantum limit (standard quantum limit) for feedback oscillator stability.
- It provides a pathway to engineer sub-standard quantum limit oscillators using quantum techniques.
- This work clarifies fundamental quantum limitations and opportunities in oscillator design.
Related Concept Videos
01:30Oscillations In An LC Circuit
2.3K
An idealized LC circuit of zero resistance can oscillate without any source of emf by shifting the energy stored in the circuit between the electric and magnetic fields. In such an LC circuit, if the capacitor contains a charge q before the switch is closed, then all the energy of the circuit is initially stored in the electric field of the capacitor. This energy is given by
2.3K
01:07Damped Oscillations
5.7K
In the real world, oscillations seldom follow true simple harmonic motion. A system that continues its motion indefinitely without losing its amplitude is termed undamped. However, friction of some sort usually dampens the motion, so it fades away or needs more force to continue. For example, a guitar string stops oscillating a few seconds after being plucked. Similarly, one must continually push a swing to keep a child swinging on a playground.
Although friction and other non-conservative...
Although friction and other non-conservative...
5.7K
01:24Effects of feedback
573
Feedback in control systems plays a critical role in shaping various operational parameters, extending beyond simple error reduction to influence stability, bandwidth, gain, impedance, and sensitivity. Understanding these effects requires examining a basic feedback system characterized by defined input, output, error, and feedback signals.
Feedback significantly modifies the gain of a control system. The gain of a system without feedback is altered by a factor of one plus GH, where G represents...
Feedback significantly modifies the gain of a control system. The gain of a system without feedback is altered by a factor of one plus GH, where G represents...
573
01:18Positive and Negative Feedback Loops
19.3K
Animal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis ("steady state"). Examples of these changes include regulation of the level of glucose or calcium in the blood or internal responses to external temperatures. Homeostasis requires maintaining an internal dynamic equilibrium:
19.3K
01:06Forced Oscillations
6.6K
When an oscillator is forced with a periodic driving force, the motion may seem chaotic. The motions of such oscillators are known as transients. After the transients die out, the oscillator reaches a steady state, where the motion is periodic, and the displacement is determined.
6.6K
01:04Oscillations about an Equilibrium Position
5.4K
Stability is an important concept in oscillation. If an equilibrium point is stable, a slight disturbance of an object that is initially at the stable equilibrium point will cause the object to oscillate around that point. For an unstable equilibrium point, if the object is disturbed slightly, it will not return to the equilibrium point. There are three conditions for equilibrium points—stable, unstable, and half-stable. A half-stable equilibrium point is also unstable, but is named so...
5.4K