A team at the University of Copenhagen Niels Bohr Institute has released a hybrid quantum network that greatly improves the accuracy of sensors used in fields ranging from gravitational wave astronomy to biomedical diagnosis.
Their system is published in natureleveraging entangled light and adjustable atom rotation sets to suppress quantum noise over a wide frequency range, which exceeds the so-called sensitivity beyond the standard quantum limits, which have long limited measurement techniques.
How quantum networks work
The core of the advancement is the clever combination of two quantum techniques: the frequency extrusion of light and the “negative mass” atomic spin system. The extruded light is designed to reduce its quantum noise in a property such as amplitude or phase, but the Copenhagen team’s approach allows this reduced noise to move dynamically over frequency. This is achieved by extruded light sent by a cloud of cesarean atoms, which can adjust its collective rotation to rotate the light phase according to its frequency.
The atomic spins as a whole can even reversal the signs of noise, allowing the system to simultaneously suppress interference caused by measurement (reaction noise) and uncertainty in the measurement itself (detection noise). As Professor Eugene Polzik explained in the study: “The sensor and spin system interact with two entangled beams. After interaction, two beams are detected and the detected signals are combined. The result is that the broadband signal detects broadband signals that exceed the limits of standard quantum sensitivity.”
Why this matters: compact, versatile and powerful
Traditional methods of implementing frequency-dependent extrusion, such as those used in gravitational detectors, such as Ligo, remeasures a huge, complex optical setup with a length of hundreds of meters. The new system achieves similar performance on the desktop, opening the door for more practical and widely used doors.
- Broadband quantum reduction reduction: The system suppresses octave quantum noise in the acoustic frequency range, which is crucial for applications where MRI is detected from gravity waves.
- Flexible wavelength targeting: Entangled light sources can be adjusted over a wide spectrum to adapt them to different sensing technologies.
- Compact design: The entire setup fits a standard laboratory table, unlike the dial-meter filter cavity in the current observatory.
- The potential of quantum communication: Architecture can be used in quantum repeaters and quantum memory, thereby enhancing secure long-distance communication.
Key Experiment Details
The researchers generated light (EPR) states of Einstein-Podotesky Noble (EPR) at two wavelengths: 1,064 nm (signal) and 852 nm (iDler). The idler wheel interacts with the cesarean atomic rotation ensemble, which can be tuned into a positive mass oscillator. By carefully controlling the phase of the magnetic field and light, the team exhibits frequency-dependent conditional extrusion, reducing quantum noise below the shooting noise limit on the broadband.
A significant technical achievement not highlighted in the press release is that the system is able to maintain quantum noise-limited performance until the gravitational wave backward advantage regime. The 8 cm long atomic cells used in the experiments provide phase rotation equivalent to a 5-meter-long optical filter, and with further adjustments, it can be expanded to 10 meters, an impressive feat of this compact device.
Looking to the future: From the universe to the clinic
The versatility of hybrid quantum networks means it can quickly enhance the sensitivity of gravitational wave detectors, allowing scientists to detect faint signals from cosmic events such as black hole mergers. Medically, it can improve the resolution of MRI scans or enable early detection of neurological diseases. The system’s architecture also laid the foundation for advances in quantum communication and distributed quantum sensing.
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