Sideband cooling beyond the quantum backaction limit with squeezed light

Abstract

Quantum fluctuations of the electromagnetic vacuum produce measurable physical effects such as Casimir forces and the Lamb shift [1]. Similarly, these fluctuations also impose an observable quantum limit to the lowest temperatures that can be reached with conventional laser cooling techniques [2,3]. As laser cooling experiments continue to bring massive mechanical systems to unprecedented temperatures [4,5], this quantum limit takes on increasingly greater practical importance in the laboratory [6]. Fortunately, vacuum fluctuations are not immutable, and can be "squeezed" through the generation of entangled photon pairs. Here we propose and experimentally demonstrate that squeezed light can be used to sideband cool the motion of a macroscopic mechanical object below the quantum limit. To do so, we first cool a microwave cavity optomechanical system with a coherent state of light to within 15% of this limit. We then cool by more than 2 dB below the quantum limit using a squeezed microwave field generated by a Josephson Parametric Amplifier (JPA). From heterodyne spectroscopy of the mechanical sidebands, we measure a minimum thermal occupancy of 0.19 ± 0.01 phonons. With this novel technique, even low frequency mechanical oscillators can in principle be cooled arbitrarily close to the motional ground state, enabling the exploration of quantum physics in larger, more massive systems.Rapid progress in the control and measurement of massive mechanical oscillators has enabled tests of fundamental physics, as well as applications in sensing and quantum information processing [7]. The noise performance of these experiments, however, is often limited by thermal motion of the mechanical mode. Although the most sophisticated refrigeration technologies can be sufficient for cooling high frequency mechanical structures to the ground state [8,9], observing quantum behavior in lower frequency mechanical systems requires other cooling methods. Recent efforts using active quantum feedback have been remarkably successful in preparing motional states with low entropies [10]. Thus far, however, only laser cooling techniques similar to those that revolutionized the coherent control of atomic systems [11,12] have yielded thermal occupancies below one quantum [4][5][6]. Nevertheless, vacuum fluctuations impose a lowest possible temperature that can be achieved using these techniques [2,3]. This limit is now being encountered in state of the art experiments involving macroscopic oscillators [6].The concept of sideband cooling relies on the removal of mechanical energy by scattering incident drive photons to higher frequencies. In general, however, this photon up-conversion (anti-Stokes) process competes with a downconversion (Stokes) process that adds energy to the mechanical system. In cavity optomechanics [7], a light-matter interaction arises due to a parametric modulation of an optical cavity's resonance frequency with a mechanical oscillator's position. When the cavity is driven at detuning ∆ below its resonance frequency, the dif...

Magnetic Resonance with Squeezed Microwaves

“…Microwave squeezed states [20] can then provide a sizable noise reduction, thus improving measurement sensitivity for qubit state readout [21][22][23][24] and nanomechanical resonator motion detection [25]. They have also been investigated for their effect on the dynamics of quantum systems, such as two-level atoms [26][27][28] or mechanical oscillators [29]. Here, we propose and demonstrate a novel application of quantum squeezing at microwave frequencies to magnetic resonance spectroscopy for improving the detection sensitivity of a small ensemble of electronic spins.…”

Quantum acoustics with superconducting qubits

“…The majority of demonstrations have involved megahertz frequency micromechanical oscillators parametrically coupled to gigahertz frequency electromagnetic resonators 11,12 . Because both electrical and mechanical modes are linear, these systems only allows for the generation of Gaussian states of mechanical motion.…”

“…These mechanical objects have important practical applications in the fields of quantum information and metrology as quantum memories or transducers for measuring and connecting different types of quantum systems. In pursuit of such macroscopic quantum phenomena, mechanical oscillators have been interfaced with quantum devices such as optical cavities and superconducting circuits [10][11][12] . In particular, there have been a few experiments that couple motion to nonlinear quantum objects [13][14][15] such as superconducting qubits.…”

Nonlinear effects in modulated quantum optomechanics

“…For example, considerable achievements have been achieved including cooling the mechanical modes to their quantum ground state [4][5][6], the observations of normalmode splitting [7,8], optomechanically induced transparency [9][10][11], the coherent-state conversion between cavity and mechanical modes [12][13][14], and a generation of squeezed light [15][16][17]. Note that the above achievements are realized in the strong driven optomechanical system (OMS), in which the optomechanical interactions are enhanced by a factor √ n (n is the mean photon number in the cavity) at the cost of linearizing original radiationpressure coupling.…”