A minimal observable length is a common feature of theories that aim to merge quantum physics and gravity. Quantum mechanically, this concept is associated with a nonzero minimal uncertainty in ...position measurements, which is encoded in deformed commutation relations. In spite of increasing theoretical interest, the subject suffers from the complete lack of dedicated experiments and bounds to the deformation parameters have just been extrapolated from indirect measurements. As recently proposed, low-energy mechanical oscillators could allow to reveal the effect of a modified commutator. Here we analyze the free evolution of high-quality factor micro- and nano-oscillators, spanning a wide range of masses around the Planck mass mP (≈ 22 μg). The direct check against a model of deformed dynamics substantially lowers the previous limits on the parameters quantifying the commutator deformation.
Different approaches to quantum gravity, such as string theory1, 2 and loop quantum gravity, as well as doubly special relativity3 and gedanken experiments in black-hole physics4, 5, 6, all indicate ...the existence of a minimal measurable length7, 8 of the order of the Planck length, . This observation has motivated the proposal of generalized uncertainty relations, which imply changes in the energy spectrum of quantum systems. As a consequence, quantum gravitational effects could be revealed by experiments able to test deviations from standard quantum mechanics9, 10, 11, such as those recently proposed on macroscopic mechanical oscillators12. Here we exploit the sub-millikelvin cooling of the normal modes of the ton-scale gravitational wave detector AURIGA, to place an upper limit for possible Planck-scale modifications on the ground-state energy of an oscillator. Our analysis calls for the development of a satisfactory treatment of multi-particle states in the framework of quantum gravity models. PUBLICATION ABSTRACT
A search for a new scalar field, called moduli, has been performed using the cryogenic resonant-mass AURIGA detector. Predicted by string theory, moduli may provide a significant contribution to the ...dark matter (DM) component of our Universe. If this is the case, the interaction of ordinary matter with the local DM moduli, forming the Galaxy halo, will cause an oscillation of solid bodies with a frequency corresponding to the mass of moduli. In the sensitive band of AURIGA, some 100 Hz at around 1 kHz, the expected signal, with Q=△f/f∼10^{6}, is a narrow peak, △f∼1 mHz. Here the detector strain sensitivity is h_{s}∼2×10^{-21} Hz^{-1/2}, within a factor of 2. These numbers translate to upper limits at 95% C.L. on the moduli coupling to ordinary matter (d_{e}+d_{m_{e}})≲10^{-5} around masses m_{ϕ}=3.6×10^{-12} eV, for the standard DM halo model with ρ_{DM}=0.3 GeV/cm^{3}.
We have recently shown that the very low mechanical energy achieved and measured in the main vibration mode of gravitational wave bar detectors can set an upper limit to possible modifications of the ...Heisenberg uncertainty principle that are expected as an effect of gravity. Here we give more details on the data analysis procedure that allows one to deduce the energy of the bar mode (i.e., the meaningful parameter for our purpose). Furthermore, we extend the analysis of our results, discussing their implication for physical models that face quantum gravity from different points of view, e.g., proposing modified commutation relations or exploring spacetime discreteness.
Phenomenological models aiming to join gravity and quantum mechanics often predict effects that are potentially measurable in refined low-energy experiments. For instance, modified commutation ...relations between position and momentum, that account for a minimal scale length, yield a dynamics that can be codified in additional Hamiltonian terms. When applied to the paradigmatic case of a mechanical oscillator, such terms, at the lowest order in the deformation parameter, introduce a weak intrinsic nonlinearity and, consequently, deviations from the classical trajectory. This point of view has stimulated several experimental proposals and realizations, leading to meaningful upper limits to the deformation parameter. All such experiments are based on classical mechanical oscillators, i.e., excited from a thermal state. We remark indeed that decoherence, that plays a major role in distinguishing the classical from the quantum behavior of (macroscopic) systems, is not usually included in phenomenological quantum gravity models. However, it would not be surprising if peculiar features that are predicted by considering the joined roles of gravity and quantum physics should manifest themselves just on purely quantum objects. On the basis of this consideration, we propose experiments aiming to observe possible quantum gravity effects on macroscopic mechanical oscillators that are preliminary prepared in a high purity state, and we report on the status of their realization.
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The problem of the stability of a cavity optomechanical system based on an oscillator having at the same time low optical and mechanical losses is addressed. As it is the aim to extend the use of ...optical squeezing as a tool for improving quantum limited displacement sensing at low frequency, a family of opto‐mechanical devices designed to work at frequencies of about 100 kHz was developed . The devices actually meet the initial design goals, but new requirements have emerged from the analysis of their behavior in optical cavities, due to the interaction between the cavity locking system and the low order normal modes of the devices.
The problem of the stability of a cavity optomechanical system based on an oscillator having at the same time low optical and mechanical losses is addressed. As it is the aim to extend the use of optical squeezing as a tool for improving quantum limited displacement sensing at low frequency, a family of opto‐mechanical devices designed to work at frequencies of about 100 kHz was developed . The devices actually meet the initial design goals, but new requirements have emerged from the analysis of their behavior in optical cavities, due to the interaction between the cavity locking system and the low order normal modes of the devices.
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