29 research outputs found
Discrete-time quadrature feedback cooling of a radio-frequency mechanical resonator
We have employed a feedback cooling scheme, which combines high-frequency
mixing with digital signal processing. The frequency and damping rate of a 2
MHz micromechanical resonator embedded in a dc SQUID are adjusted with the
feedback, and active cooling to a temperature of 14.3 mK is demonstrated. This
technique can be applied to GHz resonators and allows for flexible control
strategies.Comment: To appear in Appl. Phys. Let
Tunable backaction of a dc SQUID on an integrated micromechanical resonator
We have measured the backaction of a dc superconducting quantum interference
device (SQUID) position detector on an integrated 1 MHz flexural resonator. The
frequency and quality factor of the micromechanical resonator can be tuned with
bias current and applied magnetic flux. The backaction is caused by the Lorentz
force due to the change in circulating current when the resonator displaces.
The experimental features are reproduced by numerical calculations using the
resistively and capacitively shunted junction (RCSJ) model.Comment: Submitted to Phys. Rev. Let
Dissipative dynamics of a qubit coupled to a nonlinear oscillator
We consider the dissipative dynamics of a qubit coupled to a nonlinear
oscillator (NO) embedded in an Ohmic environment. By treating the nonlinearity
up to first order and applying Van Vleck perturbation theory up to second order
in the qubit-NO coupling, we derive an analytical expression for the
eigenstates and eigenfunctions of the coupled qubit-NO system beyond the
rotating wave approximation. In the regime of weak coupling to the thermal
bath, analytical expressions for the time evolution of the qubit's populations
are derived: they describe a multiplicity of damped oscillations superposed to
a complex relaxation part toward thermal equilibrium. The long time dynamics is
characterized by a single relaxation rate, which is maximal when the qubit is
tuned to one of the resonances with the nonlinear oscillator.Comment: 24 pages, 7 figures, 1 table; in the text between Eq. (8) and (9)
there were misprints in the published version until 3rd Dec 2009: in the
second order correction for the nonlinear oscillator and in the corresponding
relative error. The correct expressions are given here. The results of the
paper are not changed, as we consider the nonlinearity up to first order
perturbation theor
Coupling carbon nanotube mechanics to a superconducting circuit
The quantum behaviour of mechanical resonators is a new and emerging field
driven by recent experiments reaching the quantum ground state. The high
frequency, small mass, and large quality-factor of carbon nanotube resonators
make them attractive for quantum nanomechanical applications. A common element
in experiments achieving the resonator ground state is a second quantum system,
such as coherent photons or superconducting device, coupled to the resonators
motion. For nanotubes, however, this is a challenge due to their small size.
Here, we couple a carbon nanoelectromechanical (NEMS) device to a
superconducting circuit. Suspended carbon nanotubes act as both superconducting
junctions and moving elements in a Superconducting Quantum Interference Device
(SQUID). We observe a strong modulation of the flux through the SQUID from
displacements of the nanotube. Incorporating this SQUID into superconducting
resonators and qubits should enable the detection and manipulation of nanotube
mechanical quantum states at the single-phonon level
Hybrid Mechanical Systems
We discuss hybrid systems in which a mechanical oscillator is coupled to
another (microscopic) quantum system, such as trapped atoms or ions,
solid-state spin qubits, or superconducting devices. We summarize and compare
different coupling schemes and describe first experimental implementations.
Hybrid mechanical systems enable new approaches to quantum control of
mechanical objects, precision sensing, and quantum information processing.Comment: To cite this review, please refer to the published book chapter (see
Journal-ref and DOI). This v2 corresponds to the published versio
Nanomechanical motion measured with precision beyond the standard quantum limit
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. For example, if the imprecision of a measurement of an oscillator's
position is pushed below the standard quantum limit (SQL), quantum mechanics
demands that the motion of the oscillator be perturbed by an amount larger than
the SQL. Minimizing this quantum backaction noise and nonfundamental, or
technical, noise requires an information efficient measurement. Here we
integrate a microwave cavity optomechanical system and a nearly noiseless
amplifier into an interferometer to achieve an imprecision below the SQL. As
the microwave 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/rt(Hz). In addition, the demonstrated
efficient measurement is a critical step towards entangling mechanical
oscillators with other quantum systems.Comment: 5 pages, 4 figure
Superconducting Quantum Interference based Electromechanical Systems
Mechanical sensors are essential tools for the detection of small forces. This thesis presents the dc SQUID as a detector for the displacement of embedded micromechanical resonators. The device geometry and basic operating principle are described. The SQUID displacement detector reaches an excellent resolution, a factor of 1.5 below the standard quantum limit: It can detect one-third of a single vibrational quantum in a 129 kHz resonator. We use the high displacement sensitivity to perform feedback cooling of the temperature of the fundamental resonance mode by using a heterodyne discrete-time scheme. The thesis also studies the SQUID backaction: Because of the strong coupling between the SQUID and the resonator, the SQUID exerts forces on the resonator which change the resonator spring constant and damping depending on the current and flux bias of the SQUID. In the final chapter, the entire SQUID is mechanically suspended to form a torsional resonator. In this geometry, the backaction becomes so strong that the resonators goes into self-sustained oscillation. In conclusion, the results in this thesis show that the dc SQUID is an excellent displacement detector for micro-and nanomechanical resonators, but also that the SQUID-resonator interaction strongly influences the resonator dynamics.Quantum NanoscienceApplied Science