Bridging Quantum Realms: A Silicon-Based Electromechanical Interface for Extended Phonon Lifetimes

In the ever-evolving landscape of quantum information processing, the manipulation of long-lived mechanical oscillators in the quantum regime holds tremendous potential. In a groundbreaking development documented in Nature (link), researchers at the California Institute of Technology (Caltech) led by Professor Mohammad Mirhosseini have introduced an electromechanical system designed to function in the GHz-frequency band in a silicon-on-insulator platform, controlled by Quantum Machines’ OPX+. Leveraging a pioneering driving scheme based on an electrostatic field and high-impedance microwave cavities featuring TiN superinductors, the team achieved a parametrically-enhanced electromechanical coupling, which is a significant stride towards entering the strong-coupling regime. This meticulously designed cavity-mechanics system gracefully rests in the quantum ground state, extending mechanical lifetimes, and with robust coupling sets the stage for the integration of electromechanical resonators as not just components but keystones in hybrid quantum systems. In this blog post, we delve into the promising world of phonons -the quanta of energy stored in vibrations in solids- and their potential applications in storing and communicating quantum information with the help of advanced quantum control.

Phonons as Quantum Messengers: Electromechanical Coupling in Superconducting Circuits  

In quantum mechanics, the manipulation and transmission of information is continuously advancing. One intriguing avenue of exploration involves harnessing the power of phonons—the quanta of energy stored in vibrations within solids. 

Phonons offer unique advantages: at low temperatures, intrinsic mechanisms for phonon dissipation are suppressed, resulting in remarkably low acoustic loss in single crystalline materials, reducing the likelihood of decoherence and improving the coherence time of qubits. Furthermore, the inability of sound waves to propagate in a vacuum opens the door to trapping phonons, effectively suppressing environment-induced decay.

One of the standout features of phonons is their ability to interact with solid-state qubits and electromagnetic waves across a broad spectrum. As an example, in circuit QED superconduting qubits acting as artificial atoms strongly interact with MW photons in resonators. This property positions them as near-universal intermediaries for cross-platform information transfer, making them highly attractive for various quantum applications such as quantum sensors, networking, and memories.

While optomechanical experiments have successfully measured phonons with millisecond-to-second lifetimes, accessing long-lived mechanical resonances with electrical circuits has presented challenges. In the gigahertz frequency range, where proximity to superconducting qubits holds promise for quantum technologies, piezoelectricity has traditionally been the predominant mechanism for converting microwave photons to phonons. However, the limitations of hybrid material integration, sophisticated fabrication processes, and reliance on lossy poly-crystalline materials have restricted experiments to sub-microsecond mechanical lifetimes in compact devices.

To bridge this gap, researchers have focused on developing less invasive forms of electromechanical interaction. This is why at Quantum Machines we are proud to share with you the recent breakthrough of the Quantum Engineering Lab at CalTech, involving the realization of electromechanical coupling between microwave photons in a superconducting circuit and long-lived phonons, using our fast, processor-based quantum control solution, the OPX+.

Figure: Mechanical lifetime measurement of the total lifetime measured, at a probe power corresponding to a maximum of 4 phonons in the mechanical resonator. The exponential fit finds the total lifetime at 220 ± 6 μs.

Synthesizing Microwave Pulses for Optimal Results with advanced quantum control

To perform the ringdown measurements, the research team investigated its coherence properties. Their method involved stimulating the mechanical resonator with a precise pulse, meticulously tracking its free decay through an electromechanical readout.

Delving into the quantum behavior of the resonator demanded a delicate balance: maintaining a low photon count within the resonator—precisely four photons in this experiment, creating a minuscule signal on the nanovolt scale. To perform the ringdown measurements, the team utilized the advanced features of the OPX, enabling them to regulate the external readout rate by manipulating the detuning between the microwave resonator and the mechanical components. Microwave pulses, precisely matched to the mechanical mode, were used to populate the mechanical cavity.

Pulses, synthesized with the OPX+, played a crucial role in this intricate dance of precision. The team carefully selected the pulse length to ensure that the mechanical population reached a stable state. Post-pulse, the emitted power was meticulously detected within a specified interval, with signal processing carried out on the downconverted signal from a digitizer.

To capture the full spectrum of frequencies in the output pulse, the OPX emerged as the sole solution. Traditional quantum controllers fell short in processing the minute signals within the resonator’s lifetime (hundreds of microseconds). The OPX’s unique feature of real-time processing within nanoseconds proved instrumental, allowing the team to capture the entire signal in a single, efficient measurement. In the realm of quantum exploration, where time is of the essence, the OPX stands as a key enabler for unlocking the full potential of every quantum processor.

Pioneering the Quantum Frontier: Microwave-Phonon Coupling Success

The successful demonstration of electromechanical coupling between microwave photons and long-lived phonons represents a significant leap forward in the field of quantum information science. This achievement not only expands our understanding of quantum mechanics but also holds the potential to revolutionize quantum technologies, paving the way for unprecedented applications in quantum computing. 

At Quantum Machines, we stay at the forefront of the latest discoveries in the quantum realm, supporting groundbreaking research such as the one from Prof. Mirhosseini, prepared to address specific requirements with cutting-edge solutions. 

Your quantum journey, powered by innovation, begins here.