Relativistic Position Verification with Coherent States of Light

Scientists have proposed a new scheme for secure position verification, utilizing coherent states of light and principles of special relativity. This method addresses vulnerabilities in existing position verification systems, which are susceptible to spoofing and relay attacks. Position verification is crucial in numerous applications, from financial transactions to military communications, where authenticating a user's location is as important as authenticating their identity. The proposed protocol relies on sending pulses of light in coherent states from a verifier to a prover, who must respond with precise measurements of the arrival time of these pulses. The security of the scheme lies in the impossibility for an attacker, even with unlimited computational resources, to falsify their position without violating fundamental limits imposed by the speed of light. Unlike quantum methods employing entanglement or single-photon states, this approach uses coherent states, which are more robust and easier to generate and detect with current technology. The key to the protocol's security is the combination of the randomness of the sent coherent states and the strict temporal dependence of the responses. An attacker attempting to relay pulses from a false location would inevitably introduce a delay exceeding the relativistic limit, revealing the impersonation. Researchers have theoretically demonstrated that this scheme is secure against a wide range of attacks, including those exploiting quantum memory or the ability to process information instantaneously. This breakthrough has significant implications for the development of more secure and fraud-resistant global positioning systems. The ability to verify position unconditionally securely, without relying on computational assumptions or the complexity of mathematical problems, opens the door to new applications in national security, logistics, and e-commerce. Next steps include experimental implementation of the protocol to validate its practical feasibility and explore its limits in noisy environments.

New Method for Characterizing Large-Scale Quantum Systems

Researchers have developed a new method, called Error Per Circuit Layer (EPCL), to evaluate the performance of large-scale quantum systems. This approach is a significant milestone because it allows measuring the accumulated effect of noise in quantum operations without the need for costly classical simulations or structured gate sets, making it compatible with a wide variety of quantum architectures, including those with non-Clifford gates. EPCL works by applying identical random circuits to two disjoint quantum registers and measuring the overlap between their output states as a function of circuit depth. The decay of this overlap provides an estimate of the effective layer polarization. Unlike other benchmarking methods, EPCL avoids the need for classically simulating ideal output distributions or recovering a known reference state, which significantly simplifies the characterization process. Numerical simulations have shown that EPCL recovers the predicted polarization under weak local stochastic noise and remains well-described by a single-exponential decay even at stronger stochastic noise levels. Coherent errors associated with fixed entangling layers may require techniques such as Pauli twirling or randomized compiling to produce the expected decay. Experiments conducted on IBM quantum hardware with 8- and 16-qubit implementations have demonstrated clear EPCL decay, validating its utility for measuring aggregate register performance without the limitations of previous methods.

Inelastic Electroweak Dark Matter Proposed for LZ Events

A new study proposes an electroweak dark matter model that could explain the high-energy inelastic nuclear recoil events recently reported by the LUX-ZEPLIN (LZ) Collaboration. This model extends minimal electroweak dark matter with a Majorana and a Dirac multiplet, coupled through Higgs interactions, providing a predictive framework for high-energy inelastic nuclear recoils. In this scheme, electroweak symmetry breaking induces a neutral-state splitting, δ, and an off-diagonal Z interaction. For a series of coupled multiplets (such as 3M2D, 5M4D, etc.), both the splitting and the leading inelastic interaction are universal for a fixed (mχ, y), independent of the electroweak representation. The high recoil energy observed by LZ points to splittings of a few hundred keV. The fixed Z-mediated rate allows for the determination of a mass-dependent δLZ(mχ) by requiring one expected inelastic event in the LZ exposure, with a two-sided 90% Poisson band. This defines a universal region in the (mχ, y) plane. Intersecting this region with the representation-dependent thermal relic trajectories selects a benchmark for each multiplet. The corresponding electroweak representation then predicts a correlated loop-induced elastic spin-independent signal at lower recoil energies, which could be sought in future experiments.

TeV Higgsino Interpretation of LUX-ZEPLIN High-Recoil Event

A recent high-recoil event reported by the LUX-ZEPLIN (LZ) experiment has motivated a new theoretical interpretation within the framework of supersymmetry. This event, featuring a significant recoil, could be explained by the interaction of a Higgsino with a mass on the order of a TeV, characterized by a sub-MeV energy splitting between its neutral states. In the Minimal Supersymmetric Standard Model (MSSM), such a small gap in the Higgsino's neutral states, absent specific cancellations, typically implies electroweak gaugino masses on the order of $10^7$ GeV, a value much higher than the Higgsino's own mass. Researchers have proposed that a non-universal boundary condition for gaugino masses ($M_1^G/M_2^G = -3/5$) at the SU(5) Grand Unified Theory (GUT) scale could resolve this discrepancy. This condition would allow for the cancellation of leading bino and wino contributions and would be preserved under homogeneous one-loop evolution down to the Higgsino scale. This opens the possibility for a controlled tree-level solution with a wino mass near 120 TeV for a 350 keV gap, a 1.091 TeV Higgsino, and $\tan\beta = 10$. Mixed SU(5) representations that realize the required gaugino ratio have been identified. It is crucial to note that, despite this new interpretation, a full-density thermal Higgsino remains subject to published solar-capture bounds. This is because the inelastic Z coupling remains essentially unsuppressed, implying that the astrophysical and transport assumptions used in solar-capture limits are still valid for this scenario. The radiative sensitivity and spectrum consistency of this theoretical construction have been examined to ensure its viability.

Twin-photon generation in silicon nitride microresonators

Researchers have for the first time demonstrated the generation of spectrally degenerate twin-photon pairs using a silicon nitride ($\mathrm{Si_3N_4}$) microresonator at telecommunication wavelengths. This advance is significant because, while $\mathrm{Si_3N_4}$ photonic chips were already used as heralded single-photon sources, their ability to produce identical twin photons had not been proven. The technique relies on an inverse four-wave mixing (iFWM) process, where two pump photons with distinct frequencies are converted into a pair of identical twin photons. The experiment achieved a maximum coincidence-to-accidental ratio (CAR) of $5.4\pm0.6$, a key indicator of the photon source quality. In addition to twin-photon generation, the same microresonator also functioned as a heralded single-photon source via pump-degenerate spontaneous four-wave mixing (SFWM). In this mode, a spectral purity of $P=0.67\pm0.05$ and a heralded anti-bunching of $g^{(2)}_h(0)=0.0042\pm0.0015$ were obtained. These results confirm the versatility of the $\mathrm{Si_3N_4}$ platform for different quantum light generation schemes. The demonstration of both photon generation schemes on a single integrated $\mathrm{Si_3N_4}$ platform highlights the potential of this material for the development of scalable and tailored quantum light sources. This advance is crucial for applications in quantum communication, quantum computing, and quantum metrology, where the ability to generate photons with controlled properties is fundamental. Integration on silicon nitride chips offers a promising route towards compact and efficient quantum devices.