Exploring Quantum Limits: Novel Experiment to Test Quantum Theory on Massive Objects

Novel Experiment to Explore the Limits of Quantum Theory for Arbitrarily Massive Objects

Scientists have devised an experiment to test the validity of quantum theory for objects much more massive than the usual microphysical objects (atoms, molecules, etc.), beyond which the classical theory has to be used. This study can also help develop high-precision quantum sensors, which are important tools in cutting-edge quantum technologies.

Quantum Mechanics’ principles replacing Newtonian classical mechanics were developed nearly 100 years ago. Yet, several quantum foundational issues still need to be solved. For example, the boundary between the quantum mechanical microworld and the large-scale macroscopic classical world of everyday objects obeying Newtonian Laws remains unspecified. The question—up to what level the quantum mechanical principles are valid for macroscopic objects—continues to be one of the most fundamental open questions in contemporary physics.

This question is also intimately related to another hotly pursued fundamental issue– testing whether gravity is quantum mechanical.

All the proposed laboratory-based schemes seeking to demonstrate the quantum mechanical nature of gravity crucially rest on assuming the applicability of fundamental quantum principles for sufficiently massive objects.

However, the state–of–the–art demonstrations of quantum features have so far reached only up to macromolecules of masses ten thousand times the hydrogen atom. Hence, breakthrough ideas that are feasible to be implemented experimentally shortly are the need of the hour to scale up the tests of macroscopic quantum-ness to ever more massive objects.

Bose Institute, Kolkata, an autonomous institute of the Department of Science and Technology (DST), has addressed this challenge by formulating a novel procedure for demonstrating an observable signature of quantum behavior for an oscillating object like a pendulum with any large mass. In collaboration with D. Das, S. Bose (University College London), and H. Ulbricht (University of Southampton, UK), the institute has developed a method for demonstrating an observable signature of quantum behavior for an oscillating object like a pendulum.

These scientists have found a novel way to detect measurement-induced disturbance for an arbitrarily massive quantum mechanical pendulum. They have formulated an implementable scheme based on using lasers to suspend a single nanocrystal of silica (a microscopic glass bead) as it oscillates around the focal point of a small parabolic mirror carved out of a block of aluminum housed in a vacuum chamber.

In a typical classical pendulum, the bead would move regularly from point A to point B and back again, unaffected by any observation. However, a quantum pendulum should behave very differently. Its position will change depending on whether or not someone is watching. If we were to detect at any instant where the pendulum bob was, there would be an immediate change in its future behavior. Such a disturbance is an unavoidable consequence of any quantum mechanical system measurement process. The scheme proposed by these scientists would enable the detection of such measurement-induced quantum disturbance for objects much more massive than usual microphysical objects.

Given the present state-of-the-art technology, this envisaged experiment could be realizable in the coming years for systems ranging from oscillating nano-objects (like that of a grain of dust, about trillion times heavier than hydrogen atom) to oscillating mirrors having an effective mass of about 10 kg used for gravitational wave detection.

Thus, this work would pave the way for experiments providing the most emphatic demonstration of large-scale quantum-ness and would open up the possibility of leveraging such macroscopic quantum-ness for practical applications, such as by developing high-precision quantum sensors, which are key ingredients in emerging quantum technologies.

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