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...

Cavity opto-mechanics studies the coupling between a mechanical oscillator and a cavity field, with the aim to shed light on the border between classical and quantum physics. Here we report on a cavity opto-mechanical system in which a collective density excitation of a Bose-Einstein condensate is shown to serve as the mechanical oscillator coupled to the cavity field. We observe that a few photons inside the ultrahigh-finesse cavity trigger a strongly driven back-action dynamics, in quantitative agreement with a cavity opto-mechanical model. With this experiment we approach the strong coupling regime of cavity opto-mechanics, where a single excitation of the mechanical oscillator significantly influences the cavity field. The work opens up new directions to investigate mechanical oscillators in the quantum regime and quantum gases with non-local coupling.Cavity opto-mechanics has played a vital role in the conceptual exploration of the boundaries between classical and quantum-mechanical systems [1]. These fundamental questions have recently found renewed interest through the experimental progress with micro-engineered mechanical oscillators. Indeed, the demonstration of laser cooling of the mechanical mode [2,3,4,5,6,7] has been a substantial step towards the quantum regime [8,9,10].In general, light affects the motional degrees of freedom of a mechanical system through the radiation pressure force, which is caused by the exchange of momentum between light and matter. In cavity opto-mechanics the radiation pressure induced interaction between a single mode of an optical cavity and a mechanical oscillator is investigated. This interaction is mediated by the optical path length of the cavity which depends on the displacement of the mechanical oscillator.New possibilities for cavity opto-mechanics are now emerging in atomic physics by combining the tools of cavity quantum electrodynamics (QED) [11,12] with those of ultracold gases. Placing an ensemble of atoms inside a high-finesse cavity dramatically enhances the atomlight interaction since the atoms collectively couple to the same light mode [13,14,15,16,17,18]. In the dispersive regime this promises an exceedingly large optomechanical coupling strength, tying the atomic motion to the evolution of the cavity field. Recently, a thermal gas prepared in a stack of nearly two-dimensional trapping potentials has been shown to couple to the cavity field by a collective center of mass mode leading to Kerr nonlinearity at low photon numbers [16] and back-action heating induced by quantum-force fluctuations [19].A crucial goal for cavity opto-mechanical systems is the preparation of the mechanical oscillator in its ground state with no thermally activated excitations present, yet at the same time providing strong coupling to the light field. Here we use a Bose-Einstein condensate as the ground state of a mechanical oscillator and thereby collective density oscillation mechanical oscillation B A FIG. 1: (A)Cavity opto-mechanical model system. A mechanical oscillator, here...

Cavity quantum electrodynamics (cavity QED) describes the coherent interaction between matter and an electromagnetic field confined within a resonator structure, and is providing a useful platform for developing concepts in quantum information processing. By using high-quality resonators, a strong coupling regime can be reached experimentally in which atoms coherently exchange a photon with a single light-field mode many times before dissipation sets in. This has led to fundamental studies with both microwave and optical resonators. To meet the challenges posed by quantum state engineering and quantum information processing, recent experiments have focused on laser cooling and trapping of atoms inside an optical cavity. However, the tremendous degree of control over atomic gases achieved with Bose-Einstein condensation has so far not been used for cavity QED. Here we achieve the strong coupling of a Bose-Einstein condensate to the quantized field of an ultrahigh-finesse optical cavity and present a measurement of its eigenenergy spectrum. This is a conceptually new regime of cavity QED, in which all atoms occupy a single mode of a matter-wave field and couple identically to the light field, sharing a single excitation. This opens possibilities ranging from quantum communication to a wealth of new phenomena that can be expected in the many-body physics of quantum gases with cavity-mediated interactions.

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 Bose-Einstein 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 tempera-ture 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 osc...

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.