The advent of laser cooling techniques revolutionized the study of many atomic-scale systems. This has fueled progress towards quantum computers by preparing trapped ions in their motional ground state [1], and generating new states of matter by achieving BoseEinstein condensation of atomic vapors [2]. Analogous cooling techniques [3, 4] provide a general and flexible method for preparing macroscopic objects in their motional ground state, bringing the powerful technology of micromechanics into the quantum regime. Cavity optoor electro-mechanical systems achieve sideband cooling through the strong interaction between light and motion [5][6][7][8][9][10][11][12][13][14][15]. However, entering the quantum regime, less than a single quantum of motion, has been elusive because sideband cooling has not sufficiently overwhelmed the coupling of mechanical systems to their hot environments. Here, we demonstrate sideband cooling of the motion of a micromechanical oscillator to the quantum ground state. Entering the quantum regime requires a large electromechanical interaction, which is achieved by embedding a micromechanical membrane into a superconducting microwave resonant circuit. In order to verify the cooling of the membrane motion into the quantum regime, we perform a near quantumlimited measurement of the microwave field, resolving this motion a factor of 5.1 from the Heisenberg limit [3]. Furthermore, our device exhibits strong-coupling allowing coherent exchange of microwave photons and mechanical phonons [16]. Simultaneously achieving strong coupling, ground state preparation and efficient measurement sets the stage for rapid advances in the control and detection of non-classical states of motion [17,18], possibly even testing quantum theory itself in the unexplored region of larger size and mass [19]. The universal ability to connect disparate physical systems through mechanical motion naturally leads towards future methods for engineering the coherent transfer of quantum information with widely different forms of quanta.Mechanical oscillators that are both decoupled from their environment (high quality factor Q) and placed in the quantum regime could allow us to explore quantum mechanics in entirely new ways [17][18][19][20][21]. For an oscillator to be in the quantum regime, it must be possible to prepare it in its ground state, to arbitrarily manipulate its quantum state, and to detect its state near the Heisenberg limit. In order to prepare an oscillator in its ground state, its temperature T must be reduced such that k B T < Ω m , where Ω m is the resonance frequency of the oscillator, k B is Boltzmann's constant, and is the reduced Planck's constant. While higher resonance frequency modes (> 1 GHz) can meet this cooling requirement with conventional refrigeration (T < 50 mK), these stiff oscillators are difficult to control and to detect within their short mechanical lifetimes. One unique approach using passive cooling has successfully overcome these difficulties by using a piezoelectric dilatation osci...

Nanomechanical oscillators are at the heart of ultrasensitive detectors of force, mass and motion. As these detectors progress to even better sensitivity, they will encounter measurement limits imposed by the laws of quantum mechanics. If the imprecision of a measurement of the displacement of an oscillator is pushed below a scale set by the standard quantum limit, the measurement must perturb the motion of the oscillator by an amount larger than that scale. Here we show a displacement measurement with an imprecision below the standard quantum limit scale. We achieve this imprecision by measuring the motion of a nanomechanical oscillator with a nearly shot-noise limited microwave interferometer. As the interferometer is naturally operated at cryogenic temperatures, the thermal motion of the oscillator is minimized, yielding an excellent force detector with a sensitivity of 0.51 aN Hz(-1/2). This measurement is a critical step towards observing quantum behaviour in a mechanical object.

Recently, macroscopic mechanical oscillators have been coaxed into a regime of quantum behavior, by direct refrigeration [1] or a combination of refrigeration and laser-like cooling [2,3]. This exciting result has encouraged notions that mechanical oscillators may perform useful functions in the processing of quantum information with superconducting circuits [1,[4][5][6][7], either by serving as a quantum memory for the ephemeral state of a microwave field or by providing a quantum interface between otherwise incompatible systems [8,9]. As yet, the transfer of an itinerant state or propagating mode of a microwave field to and from a mechanical oscillator has not been demonstrated owing to the inability to agilely turn on and off the interaction between microwave electricity and mechanical motion. Here we demonstrate that the state of an itinerant microwave field can be coherently transferred into, stored in, and retrieved from a mechanical oscillator with amplitudes at the single quanta level. Crucially, the time to capture and to retrieve the microwave state is shorter than the quantum state lifetime of the mechanical oscillator. In this quantum regime, the mechanical oscillator can both store and transduce quantum information.Mechanical oscillators are particularly appealing for storing or transducing quantum information encoded in microwave fields, as their fabrication is compatible with, and their size similar to, superconducting quantum circuits. Indeed, a high-frequency mechanical oscillator has been combined with a superconducting qubit, demonstrating the transfer of a qubit state to the oscillator [1]. While an impressive demonstration, the few nanosecond lifetime of the oscillator, which was much shorter than the lifetime of the qubit, suggests that lower frequency oscillators with much longer lifetimes may form superior quantum memories. This is particularly true for storing the information in an itinerant mode of a microwave field, for which the characteristic time to acquire a new value is about 100 ns [10][11][12]. The penalty for working with a low-frequency oscillator is that the oscillator will not naturally be in its quantum ground state but rather a hot thermal state. For example, an oscillator with a resonance frequency of Ω m = 10 MHz in equilibrium with an environment at temperature T env = 25 mK will contain a statistically fluctuating number of quanta with average value n env ≡ [exp(k B T env /hΩ m )−1] −1 = 50 quanta. Fortunately, embedding the mechanical oscillator in a high frequency resonant circuit creates an interaction between the mechanical oscillator and itinerant microwave fields that can be used cool the oscillator to its ground state [2].Here we show that this same interaction exchanges a coherent state of an itinerant microwave field with the hot thermal state of the mechanical oscillator. This exchange simultaneously transfers the information from the itinerant microwave field to the mechanical oscillator and removes the thermal excitations from the mechanical oscillator, pre...