Nathan’s Quantum Tech Newsletter: №24 — Gravitational Quantum Sensors
This is what I’ve seen in quantum tech in the last couple of months until February 2020:
00 🗞 Focus: Gravitational Quantum Sensors
01 🗞 Tech News
10 📰 Research Highlights
11 🎲 Bonus Links
00 📰 Focus: Gravitational Quantum Sensors
LIGO and Virgo, the joint gravitational wave consortia and related detector complexes, based, respectively, in the USA (Washington State and Louisiana) and in Europe (Italy), can now measure more subtle gravitational episodes thanks to a quantum optics improvement in their devices.
A gravitational wave detector is a huge interferometer (stretching along a few kilometers), not much dissimilar to the table-top models used in an undergraduate physics laboratory class. An interferometer is a device that measures interference fringes. It is easy to picture interference in matter waves even in nature, such as looking at sea waves or the ripples of a stone thrown in a pond. For light, which is an electromagnetic wave, this is less intuitive, and it is easier to witness interference with the aid of modern devices, such as lasers. In Virgo, a laser beam is split into two, and the two resulting laser rays take different paths, along the two “arms” of the interferometer. They bump onto two mirrors, and on the way back they interfere with each other. Like giant lightsabers, although the beams seamlessly cross each other, apparently with no change, but actually interfering in phase due to the different paths each beam has taken.
In gravitational interferometers, the change in length of one of the arms is due to a modification of spacetime induced by a gravitational wave. Distant events such as the collapse of two neutron stars, or black holes, reverberate in space with ripples in spacetime. This change in length is very tiny, and for this reason a large interferometer is needed. In the future, even larger interferometers will be sent to space. Several gravitational wave detectors allow to pinpoint the target “event” in space, with triangulation. The blips in LIGO have already been used to check whether these events are accompanied with detectable light emission, opening the era of “multi-messenger astronomy”.
Quantum technology enters the picture twice through quantum optics. Classical optics studies the properties of light, and its characteristics when many photons are present. Quantum optics studies the properties of light at the single (or few) particle level. This description of light-matter interaction led Einstein to predict the mechanisms that is behind the laser itself, including the lasers used in LIGO and Virgo. Moreover, now another quantum mechanical effect, called “light squeezing”, will be used to enhance the sensitivities of these gravitational detectors.
Quantum squeezing is a macroscopic effect that allows to measure with more precision than otherwise possible a given quantity, such as the position of an object. Squeezing is derived from Heisenberg’s uncertainty principle, which states that the uncertainty in the measurement of two joint observables cannot be reduced to less than a given constant, set forth by the fabric of quantum mechanics. The trick used in quantum squeezing devices comes from the observation that while Heisenberg’s limit certifies the limit for the joint measurement sensitivities (say, position and momentum), it does not provide a constraint on either one of them can become more sensitive, at the expenses of the other one, for which the uncertainty grows proportionally.
Quantum squeezing has been mastered in table-top experiments over several decades now in research laboratories and generally relies on some non-linear optical process to occur, such as by shining laser light through a special type of crystal, whose anisotropic structure can affect the properties of light. The and it is now being injected in the laser beams of the LIGO device to reduce the uncertainty in the displacement of the mirrors produced by gravitational waves. Link
Both LIGO and Virgo reported improving their sensitivity by exploiting squeezed light produced by an optical parametric oscillator. Entangled photons were generated by this device to go beyond the so-called “standard quantum limit”. The idea is that, by injecting correlated noise in the interferometer, one can reduce the otherwise uncorrelated noise of the apparatus, given both by shot noise, arising from quantum fluctuations of the electromagnetic field (usually uncorrelated), and the noise given by the radiation pressure of light. Link
This enhancement in the gravitational setup is an application of quantum technology to sensing and metrology (which provides more precise standards for measurements). According to the EU Quantum Flagship, the open consortium coordinating the European research efforts in the forthcoming years, sensing is one of the pillars of application of quantum technology together with quantum communication, quantum computing, and the quantum simulation of physical systems. While quantum-technology applications are underway, we can already witness the deployment of quantum squeezing to the benefit of scientific discovery: expect quantum-resolution limited detection of astrophysical events, such as black hole dynamics, neutron star mergers and more, in the upcoming months and years, thanks to quantum-technology-powered gravitational-wave detectors. Link
01 🗞 Tech News
Amazon has inaugurated a quantum research infrastructure and the related software stack, named “braket”. Amazon has no public quantum hardware back-end plans, and thus may begin by relying on other providers, such as startups, including IonQ and Rigetti Computing. Braket seems to be part of Amazon Web Services (AWS) in a trend similar to that followed by other tech giants (IBM, Google), which have associated their research and development efforts in quantum computing to the research divisions but also to their cloud service practices. At the same time, the R&D endeavor of quantum computing, and the association with Caltech, highlights the fact that Amazon Research is further expanding in quantum. Link
India has decided to invest about 1.12 billion $ in quantum technology over the next five years. This is roughly double of the EU Quantum Flagship expenditure per year. Link
Two of the largest investment banks are setting up full-fledged quantum computing theory teams. To leads its own one, Goldman Sachs has hired Dr. Will Zeng, previously head of theory at Rigetti Computing, where he co-developed Quil, a quantum instruction language, and founder of the no-profit Unitary Fund, to form a team on quantum. Link
J.P. Morgan has hired Dr. Marco Pistoia, previously a researcher and master inventor at IBM Research, and one of the core developers of Qiskit Aqua, IBM Q’s applications software toolbox for quantum computing. Link
The French government unveiled a quantum initiative, in coordination with the public investment bank France BPI and the VC fund Quantonation. Link
10 📰 Research Highlights
With IBM’s OpenPulse, researchers can be granted pulse-level control of quantum hardware. One can demonstrate from home what a few decades ago would have been worth a Nobel prize. In this way, it is possible to advance a series of techniques aimed at improving the performance of quantum hardware. I also see the opportunity for quantum physics experiments from the cloud. Link
Researchers have used a DWave chip to perform a study of topological quantum effects in an open quantum system. Link
Collapse and Revival of an Artificial Atom Coupled to a Structured Photonic Reservoir. Link
Quantum reinforcement learning during human decision-making. Link
Yao.jl is a Julia-based software package for efficient and flexible quantum circuit design. Link
QuTiP 4.5.0 has been released. It features a noisy quantum circuits module and a 1D lattice dynamics module. Link
A blog post on the invention of quantum circuit electrodynamics. Link
Quantum optics with giant atoms — the first five years. Link
A Quantum Instruction Set Implemented on a Superconducting Quantum Processor. Link
11 🎲 Bonus Links
I now have set up a personal website. I am collecting there the longer articles I wrote in the newsletter and maybe in the future I’ll archive there all of this content. Link
‘How can we compete with Google?’: the battle to train quantum coders. Link
How to build a quantum computer at home — Hacker style. Link
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