Quantum technology (QT) applies quantum mechanical properties such as quantum entanglement, quantum superposition, and No-cloning theorem to quantum systems such as atoms, ions, electrons, photons, or molecules.
Quantum bit is the basic unit of quantum information. Whereas in a classical system, a bit is either in one state or the another. However, quantum qubits can exist in large number of states simultaneously, property called Superposition.
Quantum entanglement is a phenomenon where entangled particles can stay connected in the sense that the actions performed on one of the particles affects the other no matter what’s the distance between them. No-cloning theorem tells us that quantum information (qubit) cannot be copied.
Quantum computers shall bring power of massive parallel processing, equivalent of supercomputer to a single chip. Quantum communication refers to a quantum information exchange that uses photons as quantum information carriers over optical fibre or free-space channels.
Quantum Sensing exploit high sensitivity of quantum systems to external disturbances to develop highly sensitive sensors. They can measure Quantities such as time, magnetic and electrical fields, inertial forces, temperature, and many others. They employ quantum systems such as NV centers, atomic vapors, Rydberg atoms, and trapped ions.
MEMS stands for MicroElectroMechanical Systems denoting man-made mechanical elements, sensors, actuators, and electronics that were produced using microfabrication technology and are integrated on a silicon substrate. The critical structural elements are on the micrometer length scale. These MEMS can be found in several commonly used electromechanical devices, such as accelerometers for airbags, sensors, microphones, LOC’s (lab-on-a-chip), and optical switches.
Nanofabrication technology has made significant progress more recently, and it is now possible to further scale MEMS down to nanoelectromechanical systems (NEMS). NEMS is a class of devices integrating electrical and mechanical functionality on the nanoscale ( that have critical structural elements at or below 100 nm.)
Micro- and nano-electromechanical devices, referred to as MEMS and NEMS, are ubiquitous. These nanoscale machines with movable parts are used, for example, to trigger cars’ airbags following a shock. They can also be found in smartphones, allowing them to detect how to adequately display the screen for the viewer.
According to the scaling laws for nanomechanical resonators, many of their metrological properties improve when downscaled. Generally, metrological parameters (e.g. sensitivity and resolution) of MEMS/NEMS sensors improve when built-in nanomechanical resonators (i.e. beams, cantilevers) become smaller. This fact encourages for constant miniaturization of MEMS/NEMS based sensors. Recent advances in quantum technology and hardware have advanced MEMS systems to where these can now be designed and operated in the quantum regime, albeit using sophisticated quantum methods to control and measure the mechanics and requiring cryogenic systems to enable operation in the quantum ground state.
Forces of quantum origin become important at the scale of these devices shrinks; this is particularly true for the so-called Casimir force. This force leads to van der Waals interactions, which represent the sum of all intra-molecular interactions. These include attractions and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces, and are caused by correlations in the fluctuating polarisations of nearby particles.
Quantum MEMS promises exciting new opportunities for applications in quantum information processing and storage, and for quantum sensing. Applications are particularly relevant to superconducting qubits, which provide a high fidelity, scalable platform for information processing but are lacking a compact means for quantum information storage.
Superconducting qubits integrate easily with mechanical devices through the use of piezoelectric materials and combined with the recent demonstration of ultrahigh quality factor, microwave-frequency mechanical devices points to fascinating opportunities for sub-mm scale memories and sensors.
MEMS Technology for Quantum Information Processing in Atomic Arrays
Trapped atomic ions and neutral atoms provide exciting possibilities for realizing scalable quantum information processors (QIPs). The qubit is represented by a pair of internal states of these atoms, and most of the qubit manipulation is performed by using laser beams. In a traditional experiment, the laser beams are aligned to the atomic systems using conventional optics holders on an optical table. Flexible beam shifting capabilities are needed to individually address a large number of these atomic qubits in an array. Traditionally, acousto-optic and electro-optic deflectors are used to provide this capability. Duke researchers , utilized micro-electromechanical (MEMS) technology to provide highly flexible, multiplexed beam steering capability over a wide range of optical wavelengths.
MEMS-Based Beam Steering
MEMS-based beam steering has been widely developed for optical communications in last 1990’s and early 2000’s. The requirements, however, were very different for those applications. For QIP applications, the speed at which the beams must be shifted is a critical parameter. In our research we target the settling times for the beam steering to be on the order of a few microseconds, consistent with the timescales over which the atomic states remain quantum mechanically coherent.
MEMS-based beam steering system starts with a set of tilting mirrors, where the beam tilt is converted to a lateral beam shift using a Fourier lens located a focal length away from the MEMS mirror. In our approach, the x- and y-tilts are provided by two separate mirrors, each providing the steering function in one direction. The tilt motions in the two directions are optically combined in an innovative optical imaging system.
Figure 1 shows the schematic of our beam steering system. This system is capable of independently controlling two beams over a lattice of 5×5 sites with beam steering times of better than 10 microseconds. The project is jointly developed with Dr. Felix Lu at Applied Quantum Technologies, Inc.
Quantum MEMS sensors
Quantum sensing uses some nonintuitive properties of nature to measure things like time, magnetic fields, gravity, or acceleration. Quantum sensors are measuring device that takes advantage of quantum correlations, such as states in a quantum superposition or entanglement, for better sensitivity and resolution than can be obtained by classical systems. We can make quantum sensors to measure acceleration, gravity, rotation, time, pressure, temperature and electric and magnetic fields.
Toward Ultrasensitive Quantum MEMS Sensors, first time quantum states have been applied to practical micro-electro-mechanical systems
Microcantilevers—diving-board-like structures several microns in size—have found use in a variety of micro-electro-mechanical-system (MEMS) sensor systems. The structures are designed to deflect as molecules are adsorbed onto the cantilever surface, with the effect, on the scale of nanometers, measured by deflection of a low-power laser beam reflected off the cantilever.
Two quantum noise sources limit the potential sensitivity of such a system, however: the back-action noise, due to momentum transfer from individual photons, and the shot-noise limit ( SNL) , the noise level of the coherent light field itself. Both noise sources arise from the Heisenberg uncertainty principle. But while techniques exist to reduce the back-action noise, the SNL has heretofore constituted a fundamental barrier for systems based on classical optics.
In 2015, By cleverly deploying quantum correlated beams of light, researchers from the Oak Ridge National Laboratory (ORNL), USA, made the first direct measurement of microcantilever beam deflection with a noise floor below the shot-noise limit (SNL), blowing past a fundamental limitation of systems based on classical light (Optica, doi: 10.1364/OPTICA.2.000393). The researchers believe that the results could lead to “a new class of quantum MEMS sensors” that could boost the sensitivity of a variety of microcantilever-based sensor systems, such as atomic force microscopes (AFMs), previously limited by shot noise.
ORNL researchers Raphael Pooser and Benjamin Lawrie sought a way around that barrier using so-called squeezed light states. These are nonclassical states tuned to “squeeze” the inherent Heisenberg phase–amplitude uncertainty ellipse preferentially in one direction—for example, reducing the uncertainty in the amplitude direction while increasing it in the phase direction, or vice versa. Using such states, says Pooser, “we can surpass the quantum limit without violating the uncertainty principle by moving the noise out of the variable of interest and into an area that we don’t care about and don’t detect.”
To put the idea into practice, the scientists used four-wave mixing (4WM) to create twin beams with entangled spatial modes, each squeezed to reduce intensity quantum noise. Half of the split beam is reflected off of the deflected cantilever; the other half travels a different path. When the two beams re-combine on the detector, the quantum-correlated noise subtracts to yield a noise floor below the SNL.
Pooser and Lawrie report that they could achieve a noise reduction to 60 percent below the SNL using the technique. “By pushing the noise limit lower than ever before,” says Pooser, “we enable these sensors to see things they couldn’t see.” And the scientists note that their system used off-the-shelf components and a simple experimental setup that could prove readily adaptable to MEMS devices, which are already ubiquitous in sensing applications, and to emerging nano-electro-mechanical systems (NEMS). “This marks the first time quantum states have been applied to practical micro-electro-mechanical systems,” says Lawrie. “The method we used to improve sensitivity is highly compatible with existing sensing and imaging platforms.”
Stanford team shows a way to develop delicate NEMS, reported in April 2022
Reliable, compact, durable, and efficient, acoustic devices harness mechanical motion to perform useful tasks. A prime example of such a device is the mechanical oscillator. When displaced by a force – like sound, for instance – components of the device begin moving back-and-forth about their original position. Creating this periodic motion is a handy way to keep time, filter signals, and sense motion in ubiquitous electronics, including phones, computers, and watches.
Researchers have sought to bring the benefits of mechanical systems down into the extremely small scales of the mysterious quantum realm, where atoms delicately interact and behave in counterintuitive ways. Toward this end, Stanford researchers led by Amir Safavi-Naeini have demonstrated new capabilities by coupling tiny nanomechanical oscillators with a type of circuit that can store and process energy in the form of a qubit, or quantum “bit” of information. Using the device’s qubit, the researchers can manipulate the quantum state of mechanical oscillators, generating the kinds of quantum mechanical effects that could someday empower advanced computing and ultraprecise sensing systems.
With specialized equipment, Wollack and Cleland fabricated hardware components at nanometer-scale resolutions onto two silicon computer chips. The researchers then adhered the two chips together so the components on the bottom chip faced those on the top half, sandwich-style.
On the bottom chip, Wollack and Cleland fashioned an aluminum superconducting circuit that forms the device’s qubit. Sending microwave pulses into this circuit generates photons (particles of light), which encode a qubit of information in the device.
The top chip contains two nanomechanical resonators formed by suspended, bridge-like crystal structures just a few tens of nanometers – or billionths of a meter – long. The crystals are made of lithium niobate, a piezoelectric material. Materials with this property can convert an electrical force into motion, which in the case of this device means the electric field conveyed by the qubit photon is converted into a quantum (or a single unit) of vibrational energy called a phonon.
“Just like light waves, which are quantized into photons, sound waves are quantized into ‘particles’ called phonons,” said Cleland, “and by combining energy of these different forms in our device, we create a hybrid quantum technology that harnesses the advantages of both.”
The generation of these phonons allowed each nanomechanical oscillator to act like a register, which is the smallest possible data-holding element in a computer, and with the qubit supplying the data. Like the qubit, the oscillators accordingly can also be in a superposition state – they can be both excited (representing 1) and not excited (representing 0) at the same time. The superconducting circuit enabled the researchers to prepare, read out, and modify the data stored in the registers, conceptually similar to how conventional (non-quantum) computers work.
“The dream is to make a device that works in the same way as silicon computer chips, for example, in your phone or on a thumb drive, where registers store bits,” said Safavi-Naeini. “And while we can’t store quantum bits on a thumb drive just yet, we’re showing the same sort of thing with mechanical resonators.”
Beyond superposition, the connection between the photons and resonators in the device further leveraged another important quantum mechanical phenomenon called entanglement.
To demonstrate these quantum effects in the experiment, the Stanford researchers generated a single qubit, stored as a photon in the circuit on the bottom chip. The circuit was then allowed to exchange energy with one of the mechanical oscillators on the top chip before transferring the remaining information to the second mechanical device. By exchanging energy in this way – first with one mechanical oscillator, and then with the second oscillator – the researchers used the circuit as a tool to quantum mechanically entangle the two mechanical resonators with each other.
“The bizarreness of quantum mechanics is on full display here,” said Wollack. “Not only does sound come in discrete units, but a single particle of sound can be shared between the two entangled macroscopic objects, each with trillions of atoms moving – or not moving – in concert.”
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