In a quantum-noise limited system, weak-value amplification using postselection normally does not produce more sensitive measurements than standard methods for ideal detectors: the increased weak value is compensated by the reduced power due to the small postselection probability. Here, we experimentally demonstrate recycled weak-value measurements using a pulsed light source and optical switch to enable nearly deterministic weak-value amplification of a mirror tilt. Using photon counting detectors, we demonstrate a signal improvement by a factor of 4.4±0.2 and a signal-to-noise ratio improvement of 2.10±0.06, compared to a single-pass weak-value experiment, and also compared to a conventional direct measurement of the tilt. The signal-to-noise ratio improvement could reach around six for the parameters of this experiment, assuming lower loss elements.In a quantum-noise limited system, weak-value amplification using postselection normally does not produce more sensitive measurements than standard methods for ideal detectors: the increased weak value is compensated by the reduced power due to the small postselection probability. Here, we experimentally demonstrate recycled weak-value measurements using a pulsed light source and optical switch to enable nearly deterministic weak-value amplification of a mirror tilt. Using photon counting detectors, we demonstrate a signal improvement by a factor of 4.4±0.2 and a signal-to-noise ratio improvement of 2.10±0.06, compared to a single-pass weak-value experiment, and also compared to a conventional direct measurement of the tilt. The signal-to-noise ratio improvement could reach around six for the parameters of this experiment, assuming lower loss elements.

arXiv:2104.14393Physical Review LettersJun 1, 202140 citations

Studies of a low noise, laser actuated superconducting switch

Charles E. Cunningham, Blas Cabrera

A SQUID is the most sensitive magnetometer available. The sensitivity is limited by the intrinsic noise which is white at high frequencies and increases inversely with frequency below a frequency called the 1/f knee. The sensitivity above the 1/f knee is typically better than 10−10GHz−1/2, but below the 1/f knee it can be orders of magnitude worse. This is a serious problem for those measurements which are intrinsically low frequency or dc; for them it is important to circumvent the 1/f noise. A well-known technique for reducing amplifier noise is applied schematically to a SQUID in Fig. 1.1 The low frequency signal is modulated at a frequency above the 1/f knee. The SQUID sees a high frequency signal and in amplification adds white noise rather than 1/f noise. The signal from the SQUID is then demodulated, recovering the original signal. This scheme requires a high speed, low noise superconducting switch. We have developed and tested such a switch.A SQUID is the most sensitive magnetometer available. The sensitivity is limited by the intrinsic noise which is white at high frequencies and increases inversely with frequency below a frequency called the 1/f knee. The sensitivity above the 1/f knee is typically better than 10−10GHz−1/2, but below the 1/f knee it can be orders of magnitude worse. This is a serious problem for those measurements which are intrinsically low frequency or dc; for them it is important to circumvent the 1/f noise. A well-known technique for reducing amplifier noise is applied schematically to a SQUID in Fig. 1.1 The low frequency signal is modulated at a frequency above the 1/f knee. The SQUID sees a high frequency signal and in amplification adds white noise rather than 1/f noise. The signal from the SQUID is then demodulated, recovering the original signal. This scheme requires a high speed, low noise superconducting switch. We have developed and tested such a switch.

Conference on Lasers and Electro-OpticsApr 24, 19890 citations

Active isolation of transmon readout with a tunable inductive bridge

Chunyang Ding, Chuyao Tong, Paul Varosy +5 more

Scalable superconducting quantum computation requires fast, high-fidelity readout. Currently, this is assisted through cryogenic amplification of the readout signal. In traditional dispersive readout schemes, the amplifiers that are used to provide high signal-to-noise ratio also generate thermal noise that can decohere the qubits, demanding additional ferrite-based isolators to suppress this noise. Here, we integrate a chip-scale microwave switch, the tunable inductive bridge, into the readout chain of a fixed-frequency transmon. Flux-pulsing the switch, such that it transmits only during the readout, did not make a discernable difference to qubit coherence, residual excited-state population, or readout fidelity metrics. By injecting broadband noise that mimics amplifier thermal photons, we show that the switch suppresses the resulting qubit dephasing by more than $30$ ~dB, consistent with its independently measured on-off ratio, establishing it as a potential chip-based integrated replacement for readout-chain isolators.Scalable superconducting quantum computation requires fast, high-fidelity readout. Currently, this is assisted through cryogenic amplification of the readout signal. In traditional dispersive readout schemes, the amplifiers that are used to provide high signal-to-noise ratio also generate thermal noise that can decohere the qubits, demanding additional ferrite-based isolators to suppress this noise. Here, we integrate a chip-scale microwave switch, the tunable inductive bridge, into the readout chain of a fixed-frequency transmon. Flux-pulsing the switch, such that it transmits only during the readout, did not make a discernable difference to qubit coherence, residual excited-state population, or readout fidelity metrics. By injecting broadband noise that mimics amplifier thermal photons, we show that the switch suppresses the resulting qubit dephasing by more than $30$~dB, consistent with its independently measured on-off ratio, establishing it as a potential chip-based integrated replacement for readout-chain isolators.

quant-pharXiv:2610.27137Oct 21, 20260 citations

Stochastic signal enhancement in SQUIDs

Igor Kh. Kaufman, D. G. Luchinsky, P. V. E. McClintock +2 more

Czechoslovak Journal of PhysicsMay 1, 19960 citations

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~dB, consistent with its independently measured on-off ratio, establishing it as a potential chip-based integrated replacement for readout-chain isolators.