Quantum sensors are a new upcoming technology that offers to push the limits of how we can detect incredibly small signals in the DC and low RF regimes using magnetometers such as super-conducting quantum interference device (SQUID); N-V centres in Diamond, atomic vapour cells and atomic traps. All these technologies are currently being heavily invested in to push the boundaries of magnetometry for commercial applications. The quantum sensor I have been working to develop is set apart in several different aspects: unlike other quantum sensors it is very sensitive at the high RF and even 12.6 GHz microwave radiation; it has the ability to be rapidly tuned to different frequencies; due to the microwave decoupling technique we employ, the sensor is not sensitive to fluctuations in the DC field and therefore does not require bulky shielding or a laboratory environment to function. To this end I have built a demonstrator system capable of sensing RF and microwave fields and have measured the sensitivity of this device in both of these regimes. There has also been work on developing a portable version of the demonstrator and this work is ongoing within the group.
Quantum sensors are a new upcoming technology that offers to push the limits of how we can detect incredibly small signals in the DC and low RF regimes using magnetometers such as super-conducting quantum interference device (SQUID); N-V centres in Diamond, atomic vapour cells and atomic traps. All these technologies are currently being heavily invested in to push the boundaries of magnetometry for commercial applications. The quantum sensor I have been working to develop is set apart in several different aspects: unlike other quantum sensors it is very sensitive at the high RF and even 12.6 GHz microwave radiation; it has the ability to be rapidly tuned to different frequencies; due to the microwave decoupling technique we employ, the sensor is not sensitive to fluctuations in the DC field and therefore does not require bulky shielding or a laboratory environment to function. To this end I have built a demonstrator system capable of sensing RF and microwave fields and have measured the sensitivity of this device in both of these regimes. There has also been work on developing a portable version of the demonstrator and this work is ongoing within the group.
This thesis describes an ion trap magnetometer, in which experimental hardware and theory for trapped ion magnetometry has been developed and demonstrated. Quantum magnetometry has been a fast expanding field in recent years due to the plethora of military, medical and security applications. The current quantum magnetometer literature has shown great improvements on the standard magnetometer success metrics such as sensitivity, spacial resolution, frequency tuneability, noise shielding and vector field resolution. Ion trap magnetometry could potentially boast several advantages over some of the better established methods such as, nano-meter spatial resolution, broadband tuneability over radio-frequency (RF) and microwave frequencies, and magnetic field noise shielding and sensitivity improvements through dynamic decoupling methods; all in room temperature environments. The experimental setup discussed uses a micro-fabricated Paul trap for ion confinement due to the scalability of this technology. The method for sensing that was demonstrated utilises long-wavelength radiation dressed states to extend the coherence time of a single 171Yb+ ion beyond the bare states and to allow for a high level of frequency tuneability. The coherence times measured were T2 = 0:645 s for RF field sensing at 15.616 MHz and T2 = 1.153 s for microwave field sensing at 12.658466 GHz. Sensitivities of SB = 125.857 ± 26.155 pT/ vHz for RF magnetic fields and SB = 102.054 ± 11.046 pT/ vHz for microwave magnetic fields were achieved experimentally. A novel micro-fabricated Paul trap for trapping multiple ion clusters was developed to improve sensitivity values by increasing the total number of trapped ions. The design confines ions over a two-dimensional surface spanning 0.65 x 1.00 mm which would also allow for magnetic field gradient measurements. Efforts have been made to miniaturise certain experimental hardware to further the development of portable trapped ion experiments. For this, a miniaturised RF resonator that could be used for radial confinement of ions within Paul traps has been developed. At the current stage of development it is capable of applying a peak RF voltage of 114.9 V with a Q value of 70 at a resonant frequency of O/2p = 12.65 MHz.
Magnetic quantum sensors based on trapped ions utilize properties of quantum mechanics which have optimized precision and beat current limits in sensor technology. Trapped ions are highly sensitive in a large span of signal ranging from DC or static B-field to the radiofrequency range in 100s of MHz and can attain the sensitivity in the range of pT to sub pT . They are tuneable to frequencies of interest and can be used as a lock-in frequency detector. This modelling and simulation based study presents an innovative design of Surface Paul Traps, enabling the use of trapped ions as ultra-sensitive sensors for magnetic field detection and precise measurement of magnetic field gradients at a sub-millimeter spatial resolution. The novel design features multiple trapping regions, allowing for the mapping of magnetic fields across various ion-trapping zones. The study demonstrates groundbreaking advancements in ion manipulation and confinement through innovative chip architecture.
A scheme of an ultra-sensitive magnetometer in the cavity quantum electromagnonics where the intracavity microwave mode coupled to a magnonic mode via magnetic dipole interaction is proposed. It is shown that by driving both magnonic and microwave modes with external classical fields and controlling the system parameters, one can reduce the added noise of magnetic field measurement below the standard quantum limit (SQL). Surprisingly, we show that beyond the rotating wave approximation (RWA), not only the added noise can be suppressed, but also the output cavity response to the input signal can be substantially amplified in order to achieve a precise magnetic-field measurement. The sensitivity of the proposed magnetic amplifier-sensor is approximately in the order of 10−18T/Hz which is competitive compared to the current state-of-the-art magnetometers like superconducting quantum interference devices (SQUIDs) and atomic magnetometers. The advantage of the proposed sensor in comparison with the other magnetometers is its high sensitivity at room temperature and sensing in a wide range of frequency up to MHz as well as its capability to signal-response amplification.
We have fabricated arrays of High-Tc Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive detectors for Radio Frequency (RF) waves. These subwavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We used a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here, we report on a 300 SQUID series array with the loop area ranging from 6 to 60 μm2, folded in a meander line covering a 3.5 mm × 120 μm substrate area, made out of a 150 nm thick YBa2Cu3O7 film. Operating at a temperature of T = 66 K in an unshielded magnetic environment under low DC bias current (I = 60 μA) and a DC magnetic field (B = 3 μT), this SQIF can detect a magnetic field of a few picoteslas at a frequency of 1.125 GHz, which corresponds to a sensitivity of a few hundreds of fT/Hz and shows a linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative subwavelength gigahertz magnetometers.
Many quantum technologies are dual-use technologies that can introduce new capabilities to defence and security-related applications or increase their effectiveness. In particular, diamond-based quantum sensors have great potential due to the high robustness of this material in conjunction with quantum effects accessible at room temperature. The negatively charged nitrogen vacancy centre (NV-), an atomic defect within the diamond matrix, carries an electron spin that can be actively addressed and read-out via optical and electrical means at room temperature. This electron spin is highly sensitive to external magnetic fields, temperature, and pressure and thus well-suited for quantum sensing in defence and security. Nowadays, diamond is reliably produced by means of chemical vapour deposition, allowing for tailored sensor elements, such as with oriented NV centres in layers and in microstructures that are highly interesting for vector magnetometry. Sensitive magnetometry is useful in global magnetic navigation, detecting metallic objects like submarines, human-machine interfaces and more. Apart from that, radiofrequency signals are detected in real-time with GHz spectral coverage in radar analysis. Recently, the use of these diamond-based quantum sensing technologies for side-channel attacks has come into focus, for example, to gather information on implementation of algorithms for cryptosystems. These technologies are introduced along with the fabrication of the underlying diamond sensor element.
Electromagnetic warfare (EW) refers to military operations exploiting the electromagnetic spectrum, and includes transmitting and receiving information encoded in electromagnetic fields. In order to interpret such information, effective sensing systems are of great importance. For EW applications, the radio frequency (RF) spectrum is specifically relevant. Traditional RF receivers and transmitters rely on antennas and associated electronic components, whose performance is fundamentally limited by constraints imposed by the laws of classical physics. Motivated by the fundamental limitations of classical technologies, quantum technology has emerged as a strategic research area in many countries, with applications in computing, communication and sensing, and could therefore be useful in EW applications in the future. This thesis aims to investigate and compare two quantum sensing approaches: Rydberg atombased electric field sensors and nitrogen-vacancy center magnetometers. The goal is to evaluate their sensing principles, fundamental limitations and potential competitiveness compared to classical RF receivers. The work combines a literature review of published research in order to understand the underlying quantum mechanical principles enabling electromagnetic field sensing, with analytical comparisons of sensitivity and detection range. Classical receiver performance was modeled using thermal-noise-limited sensitivity, while quantum sensor performance was estimated using reported sensitivities from literature. Detection range calculations were performed under simplified assumptions to illustrate the differences between conventional and atom-based sensing approaches. The results show that current quantum sensors do not yet surpass state-of-the-art classical receivers in raw sensitivity. However, they offer several unique characteristics, including intrinsic calibration, wide frequency tunability and the possibility of direct field-based measurements without conventional impedance matching. The comparison further highlights the fundamentally different noise mechanisms governing classical and quantum sensing systems. Overall, quantum sensing represents a promising emerging technology for electromagnetic field detection. Although significant technical challenges remain, continued advances may enable future quantum sensors to complement or partially replace conventional RF sensing technologies.