Session S39: Quantum Metrology and Sensing III

Accelerating the search for dark matter with squeezed and entangled microwave fields

Accelerating the search for dark matter with squeezed and entangled microwave fields

Recent experiments show that quantum enhanced sensing methods can benefit searches for hypothetical dark matter particles such as axions and dark photons. These quantum enhanced experiments use superconducting circuits to measure and manipulate the quantum state of the microwave cavities that couple to the hypothetical dark matter. In this talk, I’ll describe several concepts that make use of entanglement and squeezing to speed up the search for dark matter. These concepts already double the quantum-limited search rate in an axion search, but with the fragile nature of squeezed states precluding much larger speed-ups. To go beyond the modest speed-ups already demonstrated, future experiments should consider quantum enhanced methods during the initial design, rather than adding them to existing experiments. Indeed, learning to use these quantum enhanced measurement concepts most effectively in dark matter searches is a new frontier of experiment design.       

Entangled sensor-networks for dark-matter axion searches

The hypothetical axion particle (of unknown mass) is a leading candidate for dark matter (DM). Many experiments search for axions with microwave cavities, where an axion may convert into a cavity photon, leading to a feeble excess in the output power of the cavity. Recent work has demonstrated that injecting squeezed vacuum into the cavity can substantially accelerate the axion search. Here, we go a step further and provide a theoretical framework to leverage the benefits of quantum squeezing in a network setting consisting of many sensor-cavities. We explore performance advantage from a local entanglement sensor network, which enjoys both coherence between the axion signals and entanglement between the sensors. Our analysis will be pertinent to next-generation DM-axion searches wishing to leverage a sensor-network and quantum resources in an optimal way. Finally, we assess the possibility of using a more exotic quantum state, the Gottesman-Kitaev-Preskill (GKP) state. Despite a constant-factor improvement in the scan-time relative to a single-mode squeezed-state in the ideal case, the advantage of employing a GKP state disappears when a practical measurement scheme is considered.   

Superconducting Nanowire Single Photon Detectors for Dark Matter Detection and High Energy Physics Applications

Superconducting Nanowire Single Photon Detectors (SNSPDs) have emerged as the most advanced detectors for time-resolved single photon counting from the UV to the mid-infrared through their unique combination of high detection efficiency, low timing jitter, and low intrinsic dark count rates. Recent developments in nanofabrication, device characterization, and modelling of fundamental device physics have pushed forward the performance of SNSPDs in their historical strengths as quantum sensors at larger active areas, lower energy thresholds, and higher maximum count rates than ever before. We discuss novel applications of such state-of-the-art SNSPDs, including high energy physics, rare event detection, and quantum metrology. In particular, we report on recent progress towards a low-mass dark matter detection experiment using n-type Gallium Arsenide targets read out with large-area SNSPDs. This direct detection experiment aims to probe several orders of magnitude of unexplored parameter space for dark matter-electron interactions.   

Towards a Graphene Josephson Junction Terahertz Single-Photon Detector

Josephson junctions with graphene weak links (GJJs) have emerged as a promising platform for the detection of single photons. Combining the exceptionally small electronic heat capacity of graphene with the strongly temperature-dependent switching of current-biased Josephson junctions, these devices are capable of operating at low photon energies, with low dark count rates, and with detection efficiencies approaching unity when coupled to an appropriate resonant structure. Here we present progress in the design, fabrication, and testing of an antenna-coupled GJJ single photon detector designed for operation at 0.8 THz. Such detectors could find important applications in future space-based far-infrared observatories and the search for dark matter axions.   

Photon Number Non-Demolition Measurement in Quantum-Enhanced Telescopy

Quantum-enhanced long-baseline interferometry aims to go beyond what is classically achievable in telescopy. We propose a quantum non-demolition measurement-based scheme that verifies which spatio-temporal modes are occupied without destroying the information about the visibility function. It can be applied in examining weak thermal sources and used to improve several existing quantum telescopy schemes. Our scheme is optimal in terms of the ancilla resources needed to perform it. We show that a successful measurement requires a maximum degree of entanglement in the ancilla state.   

No Free Quantum Fisher Information: Limitations and Opportunities in Broadband Signal Estimation

Quantum systems are exquisite sensors, with applications from magnetometry to gravitational wave detection. We consider the problem of estimating the magnitude of a signal that couples to a two-level system via $H = B \cos(\omega t)Z$. For any detection protocol, the precision achieved depends on the signal's frequency and can be quantified via the quantum Fisher information. We find a limitation on having a high sensitivity across a wide range of frequencies. In particular, we show perturbatively that for small $B$ and $T$, the quantum Fisher information accumulated over time $T$ of a single spin integrated over $\omega$ cannot exceed $2 \pi T + \mathcal{O}(B^2T^3)$ and is $\mathcal{O}(T^2)$ for long times. As a result, there is a fundamental limit on the broadband sensitivity of quantum sensors. We interpret this as a form of standard quantum limit, which applies to separable strategies but can be exceeded by entangled strategies - indeed, for $n$ particles, we give strategies that accumulate QFI $n$ times faster. We give several examples where, for $BT$ $\gtrsim$ 1 we find that the integrated QFI is sometimes substantially more than $2\pi T$, which may allow the very rapid detection of a signal with unknown frequency over a very wide bandwidth.   

Shadow Imaging with Low-Intensity Thermal Light

The ability of image reconstruction using low photon flux would be desirable for numerous scientific, commercial, and defense imaging applications. We demonstrate this ability with the Shadow imaging (SI) scheme. In this novel imaging technique, the photon noise statistics of the probe beam is manipulated after its interaction with the object. Homodyne-like detection protocol eliminates the detrimental effect of the dark noise of the CCD camera. The SI scheme was originally proposed with the squeezed vacuum probe. Here, we use thermal state probe and provide theoretical as well as experimental validation of its utility in the SI scheme. We evaluate the signal-to-noise (SNR) and identify the regimes where the SI scheme has an advantage over the classical imaging scheme. Finally, to exhibit the full potential of this scheme, we image a biological specimen on a CCD camera using fewer than 500 photons in total from a low-intensity ( ≤1 average photons) thermal probe.   

Super-resolution Quantum Imaging using Massively Entangled Multimode Squeezed Light

We present a new method for realizing super-resolution quantum imaging using massively entangled multimode squeezed light (MEMSL). Each branch of the MEMSL interacts with the object and bears the spatially varying optical phase delay. When imaging optics with finite pupil sizes are used, information is lost, ensuing the well-known Rayleigh-diffraction-limited image resolution. Thanks to the analyticity in the Fourier plane, a noiseless measurement would recover the lost information and accomplish super-resolution imaging beating the Rayleigh diffraction limit. We proved rigorously in a fully quantum formalism that (1) such information recovery is possible and (2) the information recovery can be accomplished with significantly fewer resources (light intensity) when MEMSL is used than those needed in any non-entangled or non-squeezed classical light/imaging method. Furthermore, the action of the optical loss in the imaging system that degrades the imaging performance is also rigorously analyzed and will be presented. We also suggest several bioimaging applications that can benefit tremendously from the proposed quantum imaging scheme.   

Dark matter signal enhancement with a superconducting qubit*

The signal from low mass bosonic dark matter, such as axions or hidden photons, in 5-30 GHz regime is vanishing due to the shrinking detector volume. We propose to enhance the signal rate by initializing the microwave cavity in a large n-photon Fock state to stimulate the emission of the dark matter into a photon. We use the non-linearity inherited from a superconducting qubit to create the cavity Fock states and expect to enhance the signal rate by a factor of 10 before being limited by the coherence time of the cavity. We will demonstrate novel quantum control schemes using QM OPX to implement real-time feedback and Hidden Markov Model analysis [1] to improve the experimental protocol and reduce the detector dead-time by a factor of 10.

[1] Dixit et al., Phys. Rev. Lett. 126, 141302 (2021)   

Single microwave photon detector with an absolute power sensitivity of 1*10-22 W/√Hz

Single photon counters are essential for detecting weak incoherent electromagnetic radiation. In the optical domain, they are widely used to detect spontaneous emission from individual quantum systems, with applications in fluorescence microscopy, and in numerous areas of quantum technologies. In the microwave domain, operational single photon counters have been developed recently using superconducting quantum circuits, offering novel opportunities for detecting spin fluorescence at microwave frequencies [1] or dark matter axions search.

 

The single microwave photon counter is based on a transmon qubit is irreversibly coupled to the incoming photons [2] The irreversibility of the process is provided by a 4-wave mixing interaction between the qubit, two resonators and a pump tone. The device operates at 6.98 GHz and is frequency tunable on 40 MHz around this point.

 

Here we demonstrate a record low absolute power sensitivity of 1*10^-22  W/√Hz, corresponding to a dark count rate of less than 100 clicks/s and an efficiency of 0.4.   

Quantum enhanced sensing for axion dark matter through three-wave mixing

Recent demonstrations show that a weak microwave tone at an unknown frequency can be found more rapidly by using squeezed microwave fields and single quadrature measurement. In particular this squeezed-state receiver arrangement increases the bandwidth of the measurement apparatus. This technique has been successfully applied in the search for axionic dark matter, where it yielded a factor of two increase in search rate compared to the quantum-noise-limited value. In order to further improve the search rate, we propose a method to increase the visibility bandwidth which involves dynamically varying the coupling of an axion sensitive microwave cavity to an auxiliary readout resonator using Josephson ring modulator (JRM) or related device. By varying the coupling at the sum and difference frequencies of the two modes, simultaneous exchange and amplification processes should yield a 15-fold increase in the search rate. In this talk, I will discuss the theoretical foundation for this search method and progress towards a prototype experiment.   

Withdrawn

Tunneling of magnetic vortices through a thin superconducting nanowire, i.e. quantum phase slips (QPS), can cause an insulating transition instead of the typical zero resistance state. This phenomenon is dual to Cooper pair tunneling in a Josephson junction with quantum conjugate variables the phase and the charge exchanged. The QPS nanowire may allow the realization of a very precise quantum current standard. Although the experimental realization of coherent QPS was reported [1], only weak reverse Shapiro effect-like features in superconducting nanowires were observed so far [2].

Using our millikelvin-operational silicon MOSFET platform [3], we realize an integrated tunable impedance environment for ultra-thin TiN and NbN superconducting nanowires. We present experimental QPS data, compare it with recent theoretical predictions [4], and determine the effect of the cryogenic microwave background on a QPS system [5].

The research is supported by the EU H2020 grants No 862660 & 824109 and the Academy of Finland (Centre of Excellence program: projects 336817 & 312294).  

[1] Nature 484, 355–358 (2012)

[2] Phys. Rev. Lett. 109, 187001 (2012); App. Phys. Lett., 114, 242601 (2019)

[3] Appl. Phys. Lett. 118, 164002 (2021)

[4] Phys. Rev. B 102, 144509 (2020)

[5] Phys. Rev. B 85, 012504 (2012)