Periodic Reporting for period 1 - QUCLN (Quantum control of levitated nanoparticles)
Periodo di rendicontazione: 2017-05-15 al 2019-05-14
The QUantum Control of Levitated Nanoparticle (QUCLN) project set out to explore quantum mechanics on an unprecedented mass scale. Exploiting the tools developed during the past decade in the field of optomechanics, while also developing new methods, we studied the interaction between optical fields and a dielectric nanoparticle trapped in an electrodynamic trap (i.e. a Paul trap). The main objectives of this study were to bring the levitated nanoparticle platform into the quantum regime by generating and observing quantum states of motion of the particle’s centre-of-mass motion, and to use non-interferometric techniques in these isolated systems to test conjectured models for the collapse of the quantum mechanical wavefunction.
There is an underling common motivation between these two lines of research. That is, we wanted to start to answer a seemingly simple question: does quantum mechanics provide a good description of the behaviour of systems on any mass scale by using levitated masses far larger than the typical atomic systems that we know are described by quantum mechanics?
Quantum mechanics has been placed under increasingly higher scrutiny but has always proven to provide a very accurate description of the microscopic world. Yet the question still remains, can the superposition of a system, where a particle is simultaneously in two different locations, be created at any scale and for any separation? Is there an intrinsic, yet unknown, limit to this fundamental principle of quantum mechanics?
Bringing a levitated oscillator into the quantum regime is the first necessary step toward the creation of these quantum superposition states. However, even without entering the quantum regime, there can be clues as to whether such a superposition can be realized. Indeed, a range of collapse models predict measurable effects even for classical systems.
Throughout the duration of the project we have made significant progress towards the observation of the motional ground state of a levitated nanoparticle and have made tests of collapse models. We have understood the noise and decoherence processes that prevent the creation of delicate quantum states and have developed our understanding and the tools required to mitigate them. We are now on the verge of using these methods to reach this demanding experimental regime. Even now, the technological advancements which have been made during this project have allowed us to create a charge particle nanoscale oscillator which has only very recently been used to place important new constraints on two collapse models.
There is an underling common motivation between these two lines of research. That is, we wanted to start to answer a seemingly simple question: does quantum mechanics provide a good description of the behaviour of systems on any mass scale by using levitated masses far larger than the typical atomic systems that we know are described by quantum mechanics?
Quantum mechanics has been placed under increasingly higher scrutiny but has always proven to provide a very accurate description of the microscopic world. Yet the question still remains, can the superposition of a system, where a particle is simultaneously in two different locations, be created at any scale and for any separation? Is there an intrinsic, yet unknown, limit to this fundamental principle of quantum mechanics?
Bringing a levitated oscillator into the quantum regime is the first necessary step toward the creation of these quantum superposition states. However, even without entering the quantum regime, there can be clues as to whether such a superposition can be realized. Indeed, a range of collapse models predict measurable effects even for classical systems.
Throughout the duration of the project we have made significant progress towards the observation of the motional ground state of a levitated nanoparticle and have made tests of collapse models. We have understood the noise and decoherence processes that prevent the creation of delicate quantum states and have developed our understanding and the tools required to mitigate them. We are now on the verge of using these methods to reach this demanding experimental regime. Even now, the technological advancements which have been made during this project have allowed us to create a charge particle nanoscale oscillator which has only very recently been used to place important new constraints on two collapse models.
The levitated cavity optomechanics experiment developed at UCL has been very successful in demonstrating cooling of the center of mass motion of a nanoparticle down to few hundreds of mK. To progress further we needed to carefully assess every possible noise source limiting the cooling efficiency. This led to a major redesign of the experiment to include critical upgrades. Among these, a high finesse filtering cavity, to bring the laser field closer to an ideal coherent state, and a mechanical isolation system to reduce the effects of ambient vibrational noise.
With our international colleagues, we reached the quantum mechanical ground state of a drum mode of a SiN membrane at liquid He temperatures and we developed a novel approach to optomechanics showing that even with a very low finesse cavity cooling a levitated particle to the ground state is possible provided the cavity is long enough. We have also developed and tested a new approach to optical phase sensitive detection that can provide a single-shot measurement of hundreds of different field quadratures.
In collaboration with the University of Southampton we investigated possible schemes to detect a nanoparticle levitated in a Paul trap at an extremely low temperature of 300 mK. We compared the performance of an optical cavity, an optical tweezer and a superconductive quantum interference device (SQUID) in terms of the ability to detect the effects predicted by collapse models. The article summarizing these findings has been selected as “Editor’s suggestion” by the board of Physical Review A.
We have developed a reliable source of highly charge trapped particle based on electrospray technology and a new refined design for a miniaturized linear Paul trap. This has allowed us to observe the nanoparticle motion at extremely low pressures (10-7 mbar) and measure a record low linewidth of ~80 µHz. This enabled us to place new stringent bounds on two important dissipative collapse models, namely, the continuous spontaneous localization and the Diósi-Penrose.
This project enabled us to produce and publish high-quality research, with 4 articles published in peer reviewed journals and additional 4 currently under review. These results were also presented at international conferences including the Gordon Research Conference on “Mechanical systems in the quantum regime”.
With our international colleagues, we reached the quantum mechanical ground state of a drum mode of a SiN membrane at liquid He temperatures and we developed a novel approach to optomechanics showing that even with a very low finesse cavity cooling a levitated particle to the ground state is possible provided the cavity is long enough. We have also developed and tested a new approach to optical phase sensitive detection that can provide a single-shot measurement of hundreds of different field quadratures.
In collaboration with the University of Southampton we investigated possible schemes to detect a nanoparticle levitated in a Paul trap at an extremely low temperature of 300 mK. We compared the performance of an optical cavity, an optical tweezer and a superconductive quantum interference device (SQUID) in terms of the ability to detect the effects predicted by collapse models. The article summarizing these findings has been selected as “Editor’s suggestion” by the board of Physical Review A.
We have developed a reliable source of highly charge trapped particle based on electrospray technology and a new refined design for a miniaturized linear Paul trap. This has allowed us to observe the nanoparticle motion at extremely low pressures (10-7 mbar) and measure a record low linewidth of ~80 µHz. This enabled us to place new stringent bounds on two important dissipative collapse models, namely, the continuous spontaneous localization and the Diósi-Penrose.
This project enabled us to produce and publish high-quality research, with 4 articles published in peer reviewed journals and additional 4 currently under review. These results were also presented at international conferences including the Gordon Research Conference on “Mechanical systems in the quantum regime”.
During the course of this project the experimental setup has been upgraded on almost every aspect from the increased complexity of the optical layout to the development of reliable sources of highly charged trapped nanoparticles. We have already started testing quantum mechanics at large mass scales, the core objective of the programme, but more importantly we have identified clear ways to further improve the system. As a result, reaching the quantum regime is near at hand. This will open the way to the exploration of quantum mechanics in a parameter regime previously inaccessible with the potential to uncover new physics. From a wider point of view, the collaborations established during this programme gave rise to a productive international transfer of knowledge both within Europe and overseas.