Cavity optomechanics explores the fundamental interaction between photons (light particles) and phonons (mechanical vibrations), enabling precise control and measurement of mechanical resonators at the quantum level. In a typical system, an electromagnetic field is confined within an optical or microwave cavity, which interacts with a mechanical oscillator. This interaction, named optomechanical coupling, produces measurable phenomena such as sidebands—frequency shifts that encode information about the mechanical system’s dynamics.

Ensembles of nitrogen vacancy (NV) centers in diamond make useful sensors of DC and AC magnetic fields, thanks to their ability to perform sensitive, wide field-of-view magnetic imaging at ambient conditions. By using different techniques, experimentalists can use NV centers to sense frequencies from DC up to several GHz with bandwidths of up to roughly 100 kHz. The key figure of merit for this application is the sensitivity, which specifies the weakest field strength that can be detected with a signal-to-noise ratio (SNR) of unity in a given bandwidth.

DLTS is a powerful and commonly used technique to investigate the concentration and carrier binding energy of defects in semiconductors. The technique involves measuring capacitance transients at different temperatures. The semiconductor junction is initially reverse biased to deplete the bulk of mobile charge carriers; subsequently, as the reverse bias voltage is briefly set to zero by a positive voltage pulse the empty traps are filled.

Optically pumped magnetometers (OPMs), also referred to as atomic magnetometers, are one of the most sensitive tools to probe very weak magnetic fields, with demonstrated sensitivity reaching the fT/√Hz regime. OPMs rely on the precession of a macroscopic spin state in an ensemble of (alkali) atoms in a magnetic field. The frequency of the precession, i.e., the Larmor frequency, is proportional to the magnetic field strength. Hence, the field strength can be determined by measuring the Larmor frequency or the corresponding change in the spin direction.

Sensors come in many forms to measure a variety of mechanical parameters (such as strain and position), environmental parameters(temperature, pressure and humidity) and samples (such as materials, tissue and organisms). Changes in the sensed environment lead to a corresponding variation in the sensor's impedance. This impedance variation, which comprises inductance, capacitance and resistance or the complex impedance itself, is measured to a high precision and accuracy on a short timescale appropriate for the sensor.

Rotational motion sensing is important for the automotive and aviation sectors as well as for GPS navigation and health-monitoring systems. Today, gyroscopes based on microelectromechanical systems (MEMS) technology can be miniaturized to fit into smartphones with minimal power consumption. Such systems monitor the motion of a vibrating proof mass, attached to a mounting frame through a spring-like MEMS structure, in all spatial directions. MEMS gyroscopes are often combined with accelerometers, then providing six-dimensional measurements from a single device.

Many sensing devices, including inertial and environmental sensors, can be miniaturized and operated with minimal power consumption thanks to micro-electromechanical systems (MEMS) technology. From the design board to the realization of the sensor, an essential step is the characterization of the behavior of the MEMS structure. Application-specific analog circuitry (ASIC) is often developed for this purpose, but this approach makes the iterative sensor development process cumbersome and time-consuming. A fast and comprehensive characterization method for MEMS devices is thus essential.

Laser voltage probing (LVP) and laser voltage imaging (LVI) are techniques used in electronic failure analysis to investigate single devices and full chips while they are operated in a controlled mode.

Opto-electronics combines optical and electronic material and device properties to detect, generate and control light. Opto-electronics covers a wide range of applications including LEDs, laser diodes, photodiodes and solar cells. On the one hand, electrical control of an opto-electronic device results in an optical output as in the case of LEDs. On the other hand, optically exciting a device produces an electronic signal response such as the one obtained from a photodiode. Opto-electronic devices are semiconductor-based and mainly work on the principle of direct electron-photon conversion: the semiconductor's energy gap sets the energy scale of the device's optical excitation.

Break junctions (BJs) provide a robust method for studying single molecules in ambient conditions and pave the way for building a new class of nanoelectronic devices controlled via single-molecule properties.

Magnetic susceptibility is a measure of a material's response to an external magnetic field H. Equilibrium magnetization characteristics M(H) are obtained by sweeping a DC magnetic field, whereas the magnetization's dynamic properties are captured by an AC component. For small AC excitations, the susceptibility is linearly proportional to the magnetic field.

Electrical transport measurements are a basic material characterization technique that provides insight into the scattering mechanisms and the band structure of solid-state materials. Macroscopic carrier transport, as described by quantum mechanics, is one of the most fundamental concepts for electronic material properties with prominent, gate-tunable effects in low-dimensional systems and at low temperatures.

Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) is one of the most informative techniques on the electronic structure of paramagnetic species. EPR spectroscopy is particularly suitable for the investigation of (bio)chemical systems with strongly localized spin density and their interaction with the environment. For these systems EPR provides information on the structure and dynamics and is widely used in chemistry, physics and biology.

The Hall effect appears as the potential difference induced perpendicularly to the moving charge carriers and an external magnetic field. The effect is widely used for the characterization of materials and magnetic-field sensing.

Standard scanning probe microscopy (SPM) offers high spatial resolution at the expense of poor temporal discrimination. The detection bandwidth in an atomic force microscope (AFM) rarely goes beyond 5 MHz, and the preamplifier bandwidth in an ultra-low-noise scanning tunneling microscope (STM) goes down further to a few kHz due to higher requirements on the amplification gain factor.

Scanning near-field microscopy (SNOM) is a type of scanning probe microscopy technique that measures light-matter interactions at the nanoscale to investigate local optical properties of a sample. It relies on optical near-field effects to push its resolution below the diffraction limit as obtained in conventional far-field measurements. SNOM techniques first used a tapered optical fiber to create an optical aperture, but recent years saw the development of so-called apertureless SNOM or scattering SNOM, where the incident light is scattered by a metal-coated AFM probe.

Kelvin probe force microscopy (abbreviated as KPFM, KFM or SKFM) is a technique based on atomic force microscopy (AFM) that is used to study the electronic properties of nanoscale materials and devices. KPFM quantifies the local contact potential difference (CPD) between an AFM probe and the sample surface by detecting a capacitive electrostatic force. In the case of metal surfaces, the KPFM signal is directly related to the work function of the material, while for semiconductor CPD will be related to the doping profiles of semiconductors or surface photo-voltage (SPV) of photo-sensitive thin films.

Dual-frequency resonance tracking (DFRT) is a contact mode atomic force microscopy (AFM) technique used to measure weak electrical or mechanical responses from a sample. Traditional resonance tracking techniques rely on a phase-locked loop (PLL) to keep the phase constant, but such an approach fails with ferroelectric or other materials that exhibit a phase reversal depending on the domain orientation.

Non-contact atomic force microscopy (NC-AFM), also known as dynamic force microscopy (DFM), is the AFM mode that historically has achieved the highest microscopy resolution, down to sub-atomic levels, in real space. Most NC-AFM applications are performed in ultra-high vacuum (UHV) and/or in a low-temperature environment to benefit from high Q-factor sensitivity; this is especially relevant when dealing with short-range forces or atomic-scale imaging. Tracking the resonance frequency enables a faster response compared to open-loop techniques in similar conditions, and brings in the additional advantage of quantitative resonance enhancement.

Multi-frequency techniques in atomic force microscopy (MF-AFM) can discriminate many different contributions from the tip-sample interaction in the form of mechanical, electric, magnetic, or optical responses. MF-AFM is also sensitive to non-linear effects causing a harmonic distortion from the steady-state motion of the oscillating cantilever. As most AFM sensors exhibit different eigenmodes up to a few MHz, the ability to actuate and detect such modes separately can be exploited and adapted to measure various physical phenomena.

Scanning probe microscopy (SPM) takes on different forms depending on the operating environment (ambient, liquid or vacuum), the type of measurement force under investigation (short-range or long-range), and the actuation scheme (mechanical, electrical, magnetic, or optical). SPM is a well-established high-resolution imaging tool. It features frequently in interdisciplinary projects in the fields of nanotechnology and nano-optics, and can be used to address and manipulate nano-objects such as single atoms, single molecules and quantum dots.

Tunable diode laser absorption spectroscopy (TDLAS) is one of the most common techniques to analyze the properties and constituents of gases such as concentration, temperature, pressure, and flow velocity. TDLAS measures the wavelength-dependent absorption of light through a gas medium. As the name implies, the technique usually employs a tunable-wavelength diode laser as the light source. When the wavelength of light matches one absorption line of a gas species present in the sample, the photodetector records a reduction in the light intensity. When the gas concentration is ultra-low, the induced change in transmission becomes extremely small and difficult to detect sufficiently fast. The sensitivity of TDLAS is significantly enhanced by modulating the current of the laser, which leads to a modulation of the wavelength and of the light intensity. The information about the absorption response is then recovered by demodulating the signal from the photodetector at the modulating frequency and at its second-order harmonic.

The use of lock-in amplifiers in combination with optical choppers is one of the most common low frequency lock-in amplifier applications. In order to make this a bit more interesting, James shows in the following video how to easily set up an experiment that makes use of 2 different choppers simultaneously.

THz time-domain spectroscopy is used to characterize material properties by measuring the complex frequency response within the frequency range from 0.1 THz to tens of THz. In this regime it is possible to observe various fundamental resonances, such as electronic and phononic excitations in solid-state materials.

Photoluminescence is a common technique used to characterize the optoelectronic properties of semiconductors and other materials. Its principle is simple: electrons are excited from the valence to the conductance band of the material by a laser with an energy larger than the bandgap. As a consequence, the photoexcited carriers relax and then spontaneously recombine with holes in the conduction band. In the case of direct semiconductors, the excess energy is emitted in the form of light (spontaneous emission). By analyzing the spectrum of the emitted light, it is possible to measure the material's response in terms of intensity as a function of wavelength. This gives access to information about the band structure – the bandgap width, the relative light generation efficiency, the quality of the material (inhomogeneous broadening), etc. Additional information can be gained by controlling the sample's environment, e.g., adding a magnetic field or changing the sample's temperature.

Cavity optomechanics explores the fundamental interaction between photons (light particles) and phonons (mechanical vibrations), enabling precise control and measurement of mechanical resonators at the quantum level. In a typical system, an electromagnetic field is confined within an optical or microwave cavity, which interacts with a mechanical oscillator. This interaction, named optomechanical coupling, produces measurable phenomena such as sidebands—frequency shifts that encode information about the mechanical system’s dynamics. These sidebands, known as Stokes and anti-Stokes lines, can reveal properties such as mechanical displacement, quantum states, or thermal fluctuations, making cavity optomechanics an essential tool in quantum science and sensing.

Optical phase-locked loops (OPLLs) synchronize the relative phases of two (laser) light fields. As a result, the two fields have an adjustable frequency difference while their phase relation remains constant.

The measured data can help improve the understanding of transport processes driven by phonons and electrons. In typical TDTR experiments using ultrafast laser sources, a modulated pump pulse and a subsequent time-delayed probe pulse are shone onto the sample surface. The induced thermoreflectance response is then measured as a function of the time delay between the pump and probe pulses.

Pump-probe schemes are used to measure ultrafast phenomena using short laser pulses. As the pump pulse impinges on the sample, various physical phenomena can be induced – for instance, an electronic excitation. After an adjustable time delay often controlled with an optical delay line, a probe pulse hits the sample: its transmission and/or reflection is consequently measured. By monitoring the probe signal as a function of the time delay, it is possible to obtain information on the decay dynamics of the generated excitation.

Raman spectroscopy is an analytical method that provides rich chemical information. It is particularly suitable for molecular fingerprinting of (bio)chemical systems by probing the sample’s vibrational states. It is also possible to gain information on the intermolecular interactions by controlling the environment of the sample through parameters such as its temperature. The simplicity of this method makes it possible to combine it with a microscopy technique allowing for sample imaging with chemical contrast.

Optics and photonics research aims to measure the fundamental characteristics of light and light-matter interaction on different spatial and temporal scales. With novel light sources being developed, ranging from continuous wave (CW) to pulsed ultrafast laser systems, the number of phenomena that can be studied is constantly increasing, and ever smaller effects and faster processes are being investigated.

Sensors come in many forms to measure a variety of mechanical parameters (such as strain and position), environmental parameters(temperature, pressure and humidity) and samples (such as materials, tissue and organisms). Changes in the sensed environment lead to a corresponding variation in the sensor's impedance. This impedance variation, which comprises inductance, capacitance and resistance or the complex impedance itself, is measured to a high precision and accuracy on a short timescale appropriate for the sensor. As impedance often changes with frequency, a sensor's impedance spectrum provides an additional fingerprint for the measured sample or environment. The vast array of sensors currently available includes chemical sensors and biosensors. Chemical sensors are typically capacitive: the presence of an analyte in the dielectric causes a change in the capacitance. Impedimetric biosensors are used to measure tissue or organisms in a liquid medium (static or flowing), and in most cases are non-destructive and label-free.

Supercapacitors, also known as ultracapacitors or electrochemical capacitors, are promising energy storage devices that bridge the gap between electrolytic capacitors and batteries. Thanks to their high power and long lifespan, supercapacitors are widely used in applications ranging from SRAM to high-speed trains. The key to such high performance is often a low equivalent series resistance (ESR), which reduces the energy wasted via Ohmic heating during charging and discharging cycles. Characterization of the supercapacitor impedance at different frequencies is thus important to determine the ESR and other critical device parameters. At low frequencies, such characterization sets a unique measurement challenge that requires an instrument capable of measuring current and voltage directly and of measuring impedance with high accuracy.

High-performance components are critical when developing faster and smaller electronic devices. A prime example is the capacitor, which is often called upon to ensure an extremely low equivalent series resistance (ESR). Capacitors with this property have a high quality factor Q or, equivalently, low loss or low dissipation D.

DC-link capacitors are widely used in inverter circuits to convert DC electricity back to AC. On electrical vehicles, for example, when the coupled insulated gate bipolar transistor (IGBT) switches off, a voltage spike proportional to the parasitic inductance is induced. Reducing the equivalent series inductance (ESL) of the capacitor is therefore important to prevent shock damage. Furthermore, it is desirable to have a low equivalent series resistance (ESR) to enhance the device efficiency and suppress heat dissipation. Characterization of low ESL and low ESR with an impedance analyzer is thus crucial to verify the capacitor performance over the frequency range of interest. In turn, such measurements set the benchmark for future component development.

Dielectric spectroscopy is a form of impedance spectroscopy where the dielectric properties (dielectric constant and dissipation factor) of a medium or sample are characterized as a function of frequency. A dielectric is an electrical insulator with very low conductivity at DC; because of its polarizability, however, a dielectric can store charges in the low or mid-frequency range.

Trends in biosystems engineering for cells and sub-cellular components (nucleus, RNA, DNA) have created a demand for electrical impedance spectroscopy with increased sensitivity over an ever broader range of frequencies. From the few MHz of the past, applications now extend into the high-frequency band. Furthermore, the ability to perform measurements at several frequencies simultaneously represents a clear advantage as it means that the impedance profile of a cell can be taken in real time.

DLTS is a powerful and commonly used technique to investigate the concentration and carrier binding energy of defects in semiconductors. The technique involves measuring capacitance transients at different temperatures.

Impedance measurements represent a non-destructive way to probe the properties of a material or device by injecting a sinusoidal voltage and measuring the returning current with a phase-sensitive technique. When varying the signal frequency, impedance spectroscopy yields critical information about the frequency-dependent behavior of the sample and thus provides a fundamental characterization of its dielectric properties.

Ensembles of nitrogen vacancy (NV) centers in diamond make useful sensors of DC and AC magnetic fields, thanks to their ability to perform sensitive, wide field-of-view magnetic imaging at ambient conditions. By using different techniques, experimentalists can use NV centers to sense frequencies from DC up to several GHz with bandwidths of up to roughly 100 kHz. The key figure of merit for this application is the sensitivity, which specifies the weakest field strength that can be detected with a signal-to-noise ratio (SNR) of unity in a given bandwidth. Compared to single NV centers, ensembles comprising N different NV centers in the sensing volume benefit from a √N improvement to the sensitivity, allowing them to reach sensitivities at the level of pT/√Hz.

Nitrogen vacancy (NV) centers in diamond offer a prime opportunity for coherently controlling the state of a quantum system. The spin state of the NV center can be manipulated with a sequence of optical and microwave pulses, and exhibits long coherence times even at room temperature. It can either be isolated from the environment for quantum information processing tasks or be used as a sensor of external electric or magnetic fields. Shifting the NV center's energy levels with a vector magnet allows it to operate at frequencies ranging from DC up to 20 GHz. The NV center's high degree of tunability, both in terms of its frequency range as well as its sensitivity to the environment, make it a versatile system when coupled with an experimental setup that can fully exploit its properties.

In quantum feedback measurements, the results of single-shot qubit measurements are used as decision input for an immediate feedback action on the qubits. The lower the feedback latency, the smaller the error rate of the feedback operation and the higher the fidelity of the overall quantum information processing operation. To ensure repeatability, the entire feedback loop needs to be completed with deterministic timing even when passing through multiple instruments. Quantum feedback is used in applications such as rapid qubit initialization, quantum state stabilization, and quantum error correction. Use cases differ in the complexity of the required signal processing between measurement and feedback; the signal processing step ranges from a simple forwarding of digital bits of information to demanding error syndrome decoding.

Spin-based quantum computing is a leading technology for the realization of scalable quantum computers. Semiconductor quantum dots (QDs) are used to trap individual charges and the associated spins, which are then used as qubits. The Zurich Instruments Quantum Computing Control System (QCCS) provides all the key tools for spin qubit characterization, control and readout, providing a low-noise and scalable solution that improves setup reliability and simplifies setup control.

Encoding quantum information in non-classical states of harmonic oscillators (bosonic modes) was among the first conceptual schemes for the realization of quantum computers. In the past decade, quantum control and measurement of bosonic degrees of freedom have been reliably implemented in superconducting microwave circuits with Josephson junctions. Superconducting bosonic qubits are a leading platform for demonstrating error-correctable quantum logical memories in a hardware-efficient architecture, which opens a highly innovative subfield in superconducting quantum technology.

Superconducting fluxonium qubits are among the leading qubit candidates for building useful quantum computers. Since their first realization in 2009, research on fluxonium qubits has demonstrated great progress in improving qubit coherence times, control efficiency, and coupling architectures. Following the growing number of academic research groups, the industrial startup Atlantic Quantum is the first to focus on this technology, owing to the fluxonium's exceptional potential for enabling high-fidelity qubit operations.

Superconducting qubits are one of the most promising technologies for the realization of a scalable, fault-tolerant quantum computer. Tremendous progress has been achieved over the past two decades, with major steps forward reported worldwide in university laboratories, governmental institutes and a growing number of private companies. As research and development in this area continue at an ever increasing rate, individual players must focus on their key competencies – chip fabrication and characterization, quantum system operation, qubit control or algorithm design.

Employing quantum physics for technology and fundamental research enables applications that go beyond what is possible based on classical physics. A large sensitivity to the environment, nonlocality of quantum states, and the dynamics of large entangled states are the unique properties of quantum systems that make this possible. The push for higher system coherence, scale-up in physical size and number of states, and bridging the application areas of quantum sensing, computing, communication and simulation are common themes in quantum research. Today, researchers can demonstrate exquisite control over the quantum state of spins, photons, atoms, and phonons.