Thanks to the new method, the telescope will be able to detect 60% more gravitational waves. The gravitational wave machine measures extremely small distortions in space-time, up to 10 million quadrillion widths across the width of a human hair. These values are so low that even interference from the appearance and disappearance of particles is noticeable. Today, the LIGO facility has overcome this quantum limit by “compressing” laser light. When very massive objects such as black holes collide, enormous energy is released and can cause waves in the very fabric of space-time. These waves, called gravitational waves, were predicted by Albert Einstein more than a century ago, but it was not until 2015 that scientists were able to directly detect them for the first time.
This discovery was made using the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO works by shining lasers down two long tunnels, bouncing them off mirrors, and measuring the reflection of the light. The detector can detect even the smallest distortions of the laser beam (less than the width of a proton), which indicates the presence of gravitational waves. Over the years, LIGO and other detectors have detected many gravitational wave signals. But the sensitivity of these settings has limits, dictated by the laws of quantum physics. Although vacuum, even in tubes containing LIGO lasers, is often considered to be completely empty space, this cannot be achieved in practice. Quantum fluctuations mean that particles continuously appear, exist for a fraction of a second, and then disappear again. This small “crack” of quantum noise hampers LIGO observations and places severe limitations on them. Scientists have found a way to overcome this limitation using a technique called quantum compression. This method is based on the uncertainty principle, which states that the more precisely we know one property of an object, the more accurately we know another property. A typical example is a particle bouncing around a box. If we know its exact position at any given time, we are less likely to know its momentum, and vice versa.
Researchers have used the uncertainty principle to improve laser performance. They regulate two properties of light: phase and amplitude. Using special crystals added to the system’s tubes, they “compress” the light phase so that photons reach the sensor at more predictable times. But this approach created a problem because the accuracy of measuring one parameter reduces the accuracy of measuring another. To solve this problem, a new tool was installed on LIGO: a frequency-dependent compression resonator. It allows light of different frequencies to be compressed at different ratios to achieve an optimal combination of phase and amplitude for more accurate detection of gravitational waves. Scientists can now obtain more precise results, allowing gravitational waves to be detected with greater precision.
Once beyond this quantum limit, increased precision will allow LIGO to detect 60% more gravitational waves. Virgo’s partner observatory, located in Italy, is also expected to start using frequency-dependent compression technology before the end of next year. This year, scientists using LIGO discovered a new source of gravitational waves. It becomes a “cocoon” of many different particles formed around a dying giant star.