Phonon-Number-Sensitive Electromechanics

Autor: Xizheng Ma, Konrad Lehnert, J. J. Viennot
Přispěvatelé: Joint Institute for Laboratory Astrophysics (JILA), National Institute of Standards and Technology [Gaithersburg] (NIST)-University of Colorado [Boulder], National Institute of Standards and Technology [Boulder] (NIST), Department of Physics [Boulder], University of Colorado [Boulder]
Rok vydání: 2018
Předmět:
Zdroj: Physical Review Letters
Physical Review Letters, American Physical Society, 2018, 121 (18), pp.183601-183602. ⟨10.1103/PhysRevLett.121.183601⟩
ISSN: 1079-7114
0031-9007
Popis: International audience; We use the strong intrinsic nonlinearity of a microwave superconducting qubit with a 4 GHz transition frequency to directly detect and control the energy of a micromechanical oscillator vibrating at 25 MHz. The qubit and the oscillator are coupled electrostatically at a rate of approximately 2π × 22 MHz. In this far off-resonant regime, the qubit frequency is shifted by 0.52 MHz per oscillator phonon, or about 14% of the 3.7 MHz qubit linewidth. The qubit behaves as a vibrational energy detector and from its line shape we extract the phonon number distribution of the oscillator. We manipulate this distribution by driving number state sensitive sideband transitions and creating profoundly nonthermal states. Finally, by driving the lower frequency sideband transition, we cool the oscillator and increase its ground state population up to 0.48 AE 0.13, close to a factor of 8 above its value at thermal equilibrium. These results demonstrate a new class of electromechanics experiments that are a promising strategy for quantum nondemolition measurements and nonclassical state preparation. The ability to bring manmade acoustical or mechanical structures into the quantum regime has been demonstrated in a variety of devices, from micromechanical oscillators in opto-and electromechanics experiments [1,2], to acoustic resonators in circuit quantum electrodynamics (cQED) experiments [3]. Mechanical oscillators are generally very linear harmonic oscillators at the quantum scale, and to achieve arbitrary quantum control, one needs an extrinsic nonlinearity [4]. Performing nonlinear detection is also a way to enable quantum nondemolition measurement by measuring energy instead of position or momentum [5-7]. One strategy is to use the Josephson junction used in superconducting microwave circuits. It provides a dissipa-tionless strong nonlinearity and has enabled the demonstration of landmark results in quantum science from the preparation of arbitrary quantum states of microwave light [8,9] to the demonstration of early-stage quantum computers [10,11]. By using piezoelectric materials, resonant coupling between superconducting qubits and high frequency (GHz) acoustic wave resonators has been demonstrated [3,12]. This resonant approach is, however, restricted to a small class of acoustic oscillators and loses many of the advantages of the micromechanical oscillators used in opto-and electromechanics experiments [13]. In these experiments, a wide variety of techniques have been developed and have made these mass-on-a-spring-like oscillators very versatile. They can be used to interface otherwise incompatible quantum systems such as superconducting circuits and optical light [14], they are extraordinarily sensitive detectors of force and strain [15,16], and they can be engineered to have extremely long lifetimes [17]. However, these low frequency mechanical oscillators have proven to be more challenging to couple to superconducting qubits. One strategy is to use a linear cavity to transfer nonclassical microwave fields created by a qubit to a mechanical oscillator by using the radiation pressure interaction [18,19]. This approach has to battle the incompatibility of large microwave pump powers with qubits as well as the loss during the state propagation or transfer. Low frequency mechanical oscillators have also been directly coupled to qubits [20,21], but so far the interaction strengths have been too weak to achieve control or detection of motion at the scale of few phonons. In this Letter, we directly couple a superconducting qubit to a mechanical oscillator, achieving an ultrastrong interaction of g m ≈ 2π × 22 MHz, comparable to the oscillator's resonance frequency ω m ≈ 2π × 25 MHz. Similar to quad-ratic optomechanics proposals [6], we detect the energy of the oscillator instead of its position. More precisely, a mechanical ac-Stark effect shifts the qubit frequency by 0.52 MHz per oscillator phonon, or about 14% of the 3.7 MHz qubit linewidth. The qubit line shape therefore encodes the phonon number statistics, which we extract using a Bayesian-based algorithm. The qubit-oscillator system also exhibits blue and red sideband transitions, analogous to those found in optomechanics and trapped ions systems [13,22], at the sum (blue) and difference (red) of frequencies. In contrast to optomechanics, the qubit nonlinearity makes these sideband transitions number state dependent. Using this property, we demonstrate control of populations in the Fock space with a resolution of about 7 quanta. By driving the lower frequency sideband transition, we cool the oscillator and increase its ground state PHYSICAL
Databáze: OpenAIRE
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