Writing a Technology Innovation Website – 05/02/2022
The top bracket (mechanical) is held face down to the bottom bracket (cubit) by means of a polymer adhesive.
[Imagem: Agnetta Cleland]
From classic to quantum
The central field of research in physics today involves defining the boundary between the quantum world and the classical world, since matter behaves very differently when moving from the human scale to the atomic scale.
Experiments that attempt quantum entanglement between large objects are central to these studies, to try to see if the strange behavior of quantum particles holds up in larger objects.
Now, Alex Wollack and his colleagues at Stanford University in the USA have taken these experiments to a new level – one that allows quantum mechanics to be explored using mechanical components on a large scale.
By connecting micro-mechanical nano-oscillators – tiny vibrating devices – to a large-scale circuit, the team created a device capable of storing and processing energy in the form of qubits, or quantum “bits” of information.
Using the device’s qubits, researchers can manipulate the quantum state of mechanical oscillators, generating the kinds of effects that underlie quantum computers, such as interleaving and superposition.
“Using this device, we demonstrate an important next step in trying to build quantum computers and other useful quantum devices based on mechanical systems,” said Professor Amir Safavi Naini. “We’re mainly looking to build quantum mechanical systems.”
Classic cross with quantum
The components of this unusual device are manufactured with nanometer-scale precision on two silicon wafers. The researchers then stitched the two slices together, so that the ingredients on the bottom wafer faced those on the top half, shaped like a sandwich.
On the bottom slide, Woolack and colleague Agneta Cleland created a superconducting aluminum circuit that forms the device’s qubits. Powered by microwave pulses, this circuit generates photons (particles of light) that encode the data.
Unlike traditional electronic memories, which store bits as a voltage representing 0 or 1, qubits can also represent weighted groups of 0 and 1 simultaneously, thanks to a quantum mechanics phenomenon known as superposition, where a quantum system exists in multiple quantum states at the same time. – until the system is measured, at which point it collapses at a specified value.
On the top slide, the team built two mechanical resonators, made up of suspended, bridge-like crystal structures a few tens of nanometers long. These structures are made of lithium niobate, a piezoelectric material. Materials with this property can convert electrical force into motion, which in the case of this device means that the electric field transmitted by a qubit photon is converted into a quantity (or one unit) of vibrational energy, called a phnon.
“Just like light waves, which are broken down into photons, sound waves are broken down into ‘particles’ called phnons, in detail Cleland, and by incorporating the energy of these different forms into our devices, we’ve created a hybrid quantum technology that takes advantage of the advantages of both.”
Illustration of the case of a bell, in which a unit of vibrational energy is shared between two oscillators. The system exists in two possible states simultaneously: the first possible quantum state (left of the plus sign) shows the right oscillator vibrating and the left oscillator stopping. The second potential state (right) shows vibrational energy occupying the left oscillator, with the right oscillator turned off. The device is in a superposition of both possible states, which means that each oscillator is moving and not moving at the same time.
[Imagem: Agnetta Cleland]
Overlay and entanglement
Creating these arts allows each nanomechanical oscillator to act as a register, the smallest possible data-holding element in a computer, with the details being the qubits that provide the data.
Like qubits, oscillators can also be in a superposition – they can be energized (represented 1) and deactivated (represented 0) at the same time. And they can still show quantum entanglement – or entanglement – which means what happens to one oscillator will affect the other instantly.
In turn, the accompanying superconductivity circuit allowed the researchers to prepare, read and modify data stored in registers, conceptually similar to how conventional (non-quantum) computers work.
“The weirdness of quantum mechanics is on full display here,” Wollack said. “Not only does sound come in separate units, but a single particle of sound can be shared between two entangled objects, each with trillions of atoms moving—or not moving—at the same time.”
To finally make practical calculations, the period of continuous interleaving, or coherence, should be significantly longer – in the order of seconds rather than the fractions of seconds achieved thus far. But the team is optimistic.
“The dream is to make a device that works in the same way that silicon computer chips do, for example, in your phone or on a USB storage device, where the recorders store the pieces,” said Safavi Naini. “And while we still can’t store quantum bits on a flash drive, we’re demonstrating the same kind of thing using mechanical resonators.”
Article: Quantum state preparation and tomography for synaptic mechanical resonators
Authors: I. Alex Wollack, Agenta Y. Cleland, Rachel J. Groenke, Zhaoyu Wang, Patricio Aranjuez-Arriola, Prince H.
Volume: 604, pages 463-467
DOI: 10.1038 / s41586-022-04500-y
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