Caspar Ockeloen-Korppi

Quantum Backaction Evading Measurement of Collective Mechanical Modes.

The standard quantum limit constrains the precision of an oscillator position measurement. It arises from a balance between the imprecision and the quantum backaction of the measurement. However, a measurement of only a single quadrature of the oscillator can evade the backaction and be made with arbitrary precision. Here we demonstrate quantum backaction evading measurements of a collective quadrature of two mechanical oscillators, both coupled to a common microwave cavity. The work allows for quantum state tomography of two mechanical oscillators, and provides a foundation for macroscopic mechanical entanglement and force sensing beyond conventional quantum limits.

Stabilized entanglement of massive mechanical oscillators

An entangled quantum state of two or more particles or objects exhibits some of the most peculiar features of quantum mechanics. Entangled systems cannot be described independently of each other even though they may have an arbitrarily large spatial separation. Reconciling this property with the inherent uncertainty in quantum states is at the heart of some of the most famous debates in the development of quantum theory. Nonetheless, entanglement nowadays has a solid theoretical and experimental foundation, and it is the crucial resource behind many emerging quantum technologies. Entanglement has been demonstrated for microscopic systems, such as with photons, ions, and electron spins, and more recently in microwave and electromechanical devices. For macroscopic objects, however, entanglement becomes exceedingly fragile towards environmental disturbances. A major outstanding goal has been to create and verify the entanglement between the motional states of slowly-moving massive objects. Here, we carry out such an experimental demonstration, with the moving bodies realized as two micromechanical oscillators coupled to a microwave-frequency electromagnetic cavity that is used to create and stabilise the entanglement of the centre-of-mass motion of the oscillators. We infer the existence of entanglement in the steady state by combining measurement of correlated mechanical fluctuations with an analysis of the microwaves emitted from the cavity. Our work qualitatively extends the range of entangled physical systems, with implications in quantum information processing, precision measurement, and tests of the limits of quantum mechanics.Quantum entanglement is a phenomenon whereby systems cannot be described independently of each other, even though they may be separated by an arbitrarily large distance1. Entanglement has a solid theoretical and experimental foundation and is the key resource behind many emerging quantum technologies, including quantum computation, cryptography and metrology. Entanglement has been demonstrated for microscopic-scale systems, such as those involving photons2–5, ions6 and electron spins7, and more recently in microwave and electromechanical devices8–10. For macroscopic-scale objects8–14, however, it is very vulnerable to environmental disturbances, and the creation and verification of entanglement of the centre-of-mass motion of macroscopic-scale objects remains an outstanding goal. Here we report such an experimental demonstration, with the moving bodies being two massive micromechanical oscillators, each composed of about 1012 atoms, coupled to a microwave-frequency electromagnetic cavity that is used to create and stabilize the entanglement of their centre-of-mass motion15–17. We infer the existence of entanglement in the steady state by combining measurements of correlated mechanical fluctuations with an analysis of the microwaves emitted from the cavity. Our work qualitatively extends the range of entangled physical systems and has implications for quantum information processing, precision measurements and tests of the limits of quantum mechanics.Quantum entanglement is demonstrated in a system of massive micromechanical oscillators coupled to a microwave-frequency electromagnetic cavity by driving the devices into a steady state that is entangled.

Low-Noise Amplification and Frequency Conversion with a Multiport Microwave Optomechanical Device

High-gain amplifiers of electromagnetic signals operating near the quantum limit are crucial for quantum information systems and ultrasensitive quantum measurements. However, the existing techniques have a limited gain-bandwidth product and only operate with weak input signals. Here we demonstrate a two-port optomechanical scheme for amplification and routing of microwave signals, a system that simultaneously performs high-gain amplification and frequency conversion in the quantum regime. Our amplifier, implemented in a two-cavity microwave optomechanical device, shows 41 dB of gain and has a high dynamic range, handling input signals up to

Optomechanical measurement of a millimeter-sized mechanical oscillator approaching the quantum ground state

10^{13}

Electrode configuration and electrical dissipation of mechanical energy in quartz crystal resonators

photons per second, three orders of magnitude more than corresponding Josephson parametric amplifiers. We show that although the active medium, the mechanical resonator, is at a high temperature far from the quantum limit, only 4.6 quanta of noise is added to the input signal. Our method can be readily applied to a wide variety of optomechanical systems, including hybrid optical-microwave systems, creating a universal hub for signals at the quantum level.

Theory of phase-mixing amplification in an optomechanical system

Cavity optomechanics is a tool to study the interaction between light and micromechanical motion. Here we observe optomechanical physics in a truly macroscopic oscillator close to the quantum ground state. As the mechanical system, we use a mm-sized piezoelectric quartz disk oscillator. Its motion is coupled to a charge qubit which translates the piezo-induced charge into an effective radiation–pressure interaction between the disk and a microwave cavity. We measure the thermal motion of the lowest mechanical shear mode at 7 MHz down to 30 mK, corresponding to roughly 102 quanta in a 20 mg oscillator. We estimate that with realistic parameters, it is possible to utilize the back-action cooling by the qubit in order to control macroscopic motion by a single Cooper pair. The work opens up opportunities for macroscopic quantum experiments.

Noiseless Quantum Measurement and Squeezing of Microwave Fields Utilizing Mechanical Vibrations

Mechanical resonators made with monolithic piezoelectric quartz crystals are promising for studying new physical phenomena. High mechanical quality factors (

Revealing hidden quantum correlations in an electromechanical measurement

Q

Quantum back-action evading measurement of collective mechanical modes

) exhibited by the mm-sized quartz resonators make them ideal for studying weak couplings or long timescales in the quantum regime. However, energy losses through mechanical supports pose a serious limiting factor for obtaining high quality factors. Here we investigate how the

Optomechanical measurement of a millimeter-sized mechanical oscillator near the quantum limit

Q