- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Determining complementary properties using weak-measurement: uncertainty, predictability, and disturbance
摘要： It is often said that measuring a system’s position must disturb the complementary property, momentum, by some minimum amount due to the Heisenberg uncertainty principle. Using a “weak-measurement”, this disturbance can be reduced. One might expect this comes at the cost of also reducing the measurement’s precision. However, it was recently demonstrated that a sequence consisting of a weak position measurement followed by a regular momentum measurement can probe a quantum system at a single point, with zero width, in position-momentum space. Here, we study this “joint weak-measurement” and reconcile its compatibility with the uncertainty principle. While a single trial probes the system with a resolution that can saturate Heisenberg’s limit, we show that averaging over many trials can be used to surpass this limit. The weak-measurement does not trade-away precision, but rather another type of uncertainty called “predictability” which quantifies the certainty of retrodicting the measurement’s outcome.
关键词： weak-measurement,Heisenberg uncertainty principle,phase space,predictability,quantum measurement
更新于2025-09-23 15:21:01
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Adaptive tomography of qubits: purity versus statistical fluctuations
摘要： The success of quantum information processing applications relies on accurate and efficient characterization of quantum states, especially nearly-pure states. In this work, we investigate a procedure for adaptive qubit state tomography which achieves O(1/N) scaling in accuracy for large N. We analyze the performance of the adaptive protocol on the characterization of pure, mixed and nearly-pure states, and clarify the interplay between the purity of the state and the statistical fluctuations of the measurement results. Our results highlight the subtle difference between the characterization of nearly-pure states and those of pure or highly mixed states.
关键词： quantum information processing,quantum measurement,quantum tomography
更新于2025-09-23 15:19:57
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An Efficient Quantum Sealed Bidding Auction Scheme Based on the Correlation of Genuine Five-Qubit Entangled State
摘要： In this paper, an efficient quantum sealed bidding auction scheme based on genuine five-qubit entangled state is proposed. The scheme utilizes the correlation of quantum entangled states to transmit bidding information. It can use an entangled state to transmit two bits of bidding information, which greatly improves the transmission efficiency. In order to avoid collusion between bidders and auctioneer, we introduce a semi-trusted third party Trent. His supervision during the whole auction process can help participants trust each other and reduce the possibility of internal attacks. Finally, the security of the scheme is proved, and the scheme is more economical and feasible.
关键词： Sealed bidding auction scheme,Quantum measurement,Five-qubit entangled state
更新于2025-09-19 17:13:59
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Experimental measurement of the quantum geometric tensor using coupled qubits in diamond
摘要： Geometry and topology are fundamental concepts, which underlie a wide range of fascinating physical phenomena such as topological states of matter and topological defects. In quantum mechanics, the geometry of quantum states is fully captured by the quantum geometric tensor. Using a qubit formed by an NV center in diamond, we perform the first experimental measurement of the complete quantum geometric tensor. Our approach builds on a strong connection between coherent Rabi oscillations upon parametric modulations and the quantum geometry of the underlying states. We then apply our method to a system of two interacting qubits, by exploiting the coupling between the NV center spin and a neighboring 13C nuclear spin. Our results establish coherent dynamical responses as a versatile probe for quantum geometry, and they pave the way for the detection of novel topological phenomena in solid state.
关键词： Quantum Control,Quantum Information,Quantum Measurement,Quantum Geometry,Topological Physics
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Quantum Measurement of a Mechanical Resonator at and Below the Standard Quantum Limit
摘要： Interferometric techniques to measure mechanical displacement are subject to constraints ultimately governed by quantum mechanics. In a “standard” measurement of a mechanically induced optical phase shift, there exists a trade-off between measurement imprecision and motion disturbance, known as standard quantum limit (SQL). For a mechanical resonator with susceptibility χm(Ω), this limit is SSQL(Ω) = ˉh|χm(Ω)| (ˉh reduced Planck constant), at any frequency Ω. In the last half-century, a number of systems, including advanced LIGO and ultracold atoms have progressed towards this limit, but excess sources of noise have yet prevented fully reaching the SQL. Here, we show measurements of an ultracoherent mechanical resonator performed at the SQL within 33% and, for the ?rst time, below the SQL by 1.5 dB. The latter has been possible by a non-standard measurement scheme that exploits quantum correlations between optical quadratures induced in the optomechanical device.
关键词： Standard Quantum Limit,Optomechanical Device,Quantum Measurement,Mechanical Resonator
更新于2025-09-11 14:15:04
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A Secret Information Preservation Scheme Based on Four-qubit Entangled State
摘要： With the improvement of people’s security awareness, the security of personal information has attracted more and more attention. This paper proposes a scheme that considers the preservation of personal information fundamentally. It is based on quantum cryptography. The scheme uses four-qubit entangled states and unitary operation to preserve or read information. In addition, quantum key distribution and one-time pad are used to ensure the security of message transmission. Finally, security analysis shows that the scheme is feasible.
关键词： Four-qubit entangled state,Information security,Quantum measurement,Unitary operation
更新于2025-09-11 14:15:04
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Optimal measurement strategies for the trine states with arbitrary prior probabilities
摘要： We investigate the optimal measurement strategy for state discrimination of the trine ensemble of qubit states prepared with arbitrary prior probabilities. Our approach generates the minimum achievable probability of error and also the maximum confidence strategy. Although various cases with symmetry have been considered and solution techniques put forward in the literature, to our knowledge this is only the second such closed form, analytical, arbitrary prior, example available for the minimum-error figure of merit, after the simplest and well-known two-state example.
关键词： quantum measurement,quantum communication,quantum information
更新于2025-09-10 09:29:36
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Excess Loss in Homodyne Detection Originating from Distributed Photocarrier Generation in Photodiodes
摘要： The distributed absorption of photons in photodiodes induces an excess noise in continuous-wave photodetection above the transit-time roll-off frequency. We show that it can be treated as a frequency-dependent excess optical loss in homodyne detection. This places a limit on the bandwidth of high-accuracy homodyne detection, even if an ideal photodetector circuit is available. We experimentally evaluate the excess loss in two ways: a comparison of signal gain and shot-noise gain of one-port homodyne detection and a balanced homodyne detection of squeezed light at a 500-MHz sideband. These results agree with an analytic expression we develop, where the randomness of the photoabsorption is directly modeled by an intrusion of vacuum field. At 500 MHz, we estimate the excess loss at 14% for a Si photodiode with 860-nm incident light, while the numerical simulation predicts much smaller excess loss in (In, Ga)As photodiodes with 1550 nm light.
关键词： squeezed light,photodiodes,excess noise,homodyne detection,quantum measurement
更新于2025-09-09 09:28:46
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Decomposing qubit positive-operator-valued measurements into continuous destructive weak measurements
摘要： It has been shown that any generalized measurement can be decomposed into a sequence of weak measurements corresponding to a stochastic process. However, the weak measurements may require almost arbitrary unitaries, which are unlikely to be realized by any real measurement device. Furthermore, many measurement processes are destructive, like photon counting procedures that terminate once all photons are consumed. One cannot expect to have full control of the evolution of a state under such destructive measurements, and the possible unitaries allow only a limited set of weak measurements. In this paper, we consider a qubit model of destructive weak measurements, which is a toy version of an optical cavity, in which the state of an electromagnetic ?eld mode inside the cavity leaks out and is measured destructively while the vacuum state |0? leaks into the cavity. At long times, the state of the qubit inevitably evolves to be |0?, and the only available control is the choice of measurement on the external ancilla system. Surprisingly, this very limited model can still perform an arbitrary projective measurement on the qubit in any basis, where the probability of getting an outcome satis?es the usual Born rule. Combining this method with probabilistic postprocessing, the result can be extended to any generalized measurement with commuting positive-operator-valued measurement (POVM) elements. This implies, among other results, that any two-outcome POVM on a qubit can be decomposed into a sequence of destructive weak measurements by this restricted measurement device.
关键词： quantum measurement,destructive measurements,weak measurements,qubit,POVM
更新于2025-09-04 15:30:14