Michael S. Allman

Sideband cooling of micromechanical motion to the quantum ground state

The advent of laser cooling techniques revolutionized the study of many atomic-scale systems, fuelling progress towards quantum computing with trapped ions and generating new states of matter with Bose–Einstein condensates. Analogous cooling techniques can provide a general and flexible method of preparing macroscopic objects in their motional ground state. Cavity optomechanical or electromechanical systems achieve sideband cooling through the strong interaction between light and motion. However, entering the quantum regime—in which a system has less than a single quantum of motion—has been difficult because sideband cooling has not sufficiently overwhelmed the coupling of low-frequency mechanical systems to their hot environments. Here we demonstrate sideband cooling of an approximately 10-MHz micromechanical oscillator to the quantum ground state. This achievement required a large electromechanical interaction, which was obtained by embedding a micromechanical membrane into a superconducting microwave resonant circuit. To verify the cooling of the membrane motion to a phonon occupation of 0.34 ± 0.05 phonons, we perform a near-Heisenberg-limited position measurement within (5.1 ± 0.4)h/2π, where h is Planck’s constant. Furthermore, our device exhibits strong coupling, allowing coherent exchange of microwave photons and mechanical phonons. 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, possibly even testing quantum theory itself in the unexplored region of larger size and mass. Because mechanical oscillators can couple to light of any frequency, they could also serve as a unique intermediary for transferring quantum information between microwave and optical domains.

Circuit cavity electromechanics in the strong-coupling regime

Demonstrating and exploiting the quantum nature of macroscopic mechanical objects would help us to investigate directly the limitations of quantum-based measurements and quantum information protocols, as well as to test long-standing questions about macroscopic quantum coherence. Central to this effort is the necessity of long-lived mechanical states. Previous efforts have witnessed quantum behaviour, but for a low-quality-factor mechanical system. The field of cavity optomechanics and electromechanics, in which a high-quality-factor mechanical oscillator is parametrically coupled to an electromagnetic cavity resonance, provides a practical architecture for cooling, manipulation and detection of motion at the quantum level. One requirement is strong coupling, in which the interaction between the two systems is faster than the dissipation of energy from either system. Here, by incorporating a free-standing, flexible aluminium membrane into a lumped-element superconducting resonant cavity, we have increased the single-photon coupling strength between these two systems by more than two orders of magnitude, compared to previously obtained coupling strengths. A parametric drive tone at the difference frequency between the mechanical oscillator and the cavity resonance dramatically increases the overall coupling strength, allowing us to completely enter the quantum-enabled, strong-coupling regime. This is evidenced by a maximum normal-mode splitting of nearly six bare cavity linewidths. Spectroscopic measurements of these ‘dressed states’ are in excellent quantitative agreement with recent theoretical predictions. The basic circuit architecture presented here provides a feasible path to ground-state cooling and subsequent coherent control and measurement of long-lived quantum states of mechanical motion.

Strong Loophole-Free Test of Local Realism

We performed an loophole-free test of Bells inequalities. The probability that local realism is compatible with our results is less than 5.9×10^-9.

Measurement crosstalk between two phase qubits coupled by a coplanar waveguide

We investigate measurement crosstalk in a system with two flux-biased phase qubits coupled by a resonant coplanar waveguide cavity. After qubit measurement, the superconducting phase undergoes damped oscillations in a deep anharmonic potential producing a frequency chirped voltage or crosstalk signal. We show experimentally that a coplanar waveguide cavity acts as a bandpass filter that can significantly reduce the propagation of this crosstalk signal when the qubits are far off resonance from the cavity. The transmission of the crosstalk signal

A Near-Infrared 64-pixel Superconducting Nanowire Single Photon Detector Array with Integrated Multiplexed Readout

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Low-loss superconducting resonant circuits using vacuum-gap-based microwave components

can be further minimized by reducing the qubit frequencies and the coupling capacitance to the cavity. We model the large amplitude crosstalk signal and qubit response classically with results that agree well with the experimental data. We find that the maximum energy transferred by the crosstalk generating qubit roughly saturates for long energy relaxation times

rf-SQUID-Mediated Coherent Tunable Coupling between a Superconducting Phase Qubit and a Lumped-Element Resonator

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Tripartite interactions between two phase qubits and a resonant cavity

while the delay time necessary for the crosstalk signal to propagate to the cavity scales linearly with

Quantum enigma machine: Experimentally demonstrating quantum data locking

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Coherent interactions between phase qubits, cavities, and TLS defects

. Ultimately, the use of resonant cavities as coupling elements and crosstalk filters is extremely beneficial for future architectures incorporating many coupled qubits.