1,720,988 research outputs found
A learning theory for quantum photonic processors and beyond
Full text linkWe consider the tasks of learning quantum states, measurements and channels generated by continuous-variable (CV) quantum circuits. This family of circuits is suited to describe optical quantum technologies and in particular it includes state-of-the-art photonic processors capable of showing quantum advantage. We define classes of functions that map classical variables, encoded into the CV circuit parameters, to outcome probabilities evaluated on those circuits. We then establish efficient learnability guarantees for such classes, by computing bounds on their pseudo-dimension or covering numbers, showing that CV quantum circuits can be learned with a sample complexity that scales polynomially with the circuit\u27s size, i.e., the number of modes. Our results show that CV circuits can be trained efficiently using a number of training samples that, unlike their finite-dimensional counterpart, does not scale with the circuit depth.27+5 pages, 2 figure
Multi-pulse Fourier codes for bit transmission at the quantum limit
No full textBit-transmission can be enhanced by the use of quantum detection techniques, realizing a joint-detection receiver (JDR) that is able to decode transmitted signals via a collective operation and achieve the Holevo channel capacity. Explicit JDR designs proposed so far employ the Hadamard or Fourier transform to perform a phase-to-intensity translation of the information encoding, effectively falling in the class of on-off-keying (OOK) modulation techniques; they improve over classical decoders but fall short of the Holevo capacity, particularly at large signal mean photon number n ≳ 1 . Here we introduce new families of decoders based on multi-pulse and multi-level codes. We compute the rate of these codes exactly, and provide a comprehensive study of their performance. We show that multi-pulse codes can approach the rate of OOK closely, providing a simplified design for quantum-enhanced communication in the photon-starved regime; furthermore, multi-level codes can approach generalized-OOK strategies with multiple pulse types, thus they can be employed in the larger photon-number regime
The n-shot classical capacity of the quantum erasure channel
No full textWe compute the n -shot classical capacity of the quantum erasure channel, providing upper bounds and almost-matching lower bounds for it, the latter achievable via large-minimum-distance classical linear codes for any n . The protocols are in full product form, i.e. no entanglement is needed either at the encoder or decoder to attain the capacity, and they explicitly adapt to the transition between different error regimes as the erasure probability increases. Finally, we show that our upper and lower bounds on the capacity are tighter than those obtainable from the general theory of finite-size capacity via generalized divergences
Operating Fiber Networks in the Quantum Limit
No full textWe consider all-optical network evolution from a quantum perspective. We show
that a use of optimal quantum receivers allows an estimated decrease in
energy consumption of all-optical amplifiers in network configurations that are
typical today. We then compare data transmission capacities of quantum
receivers with today's technology operating within the boundaries set by
Shannon. We find that quantum receiver technology allows for a logarithmic
scaling of the system capacity with the baud-rate, while Shannon-type systems
are limited by the transmit power. Thus a natural quantum limit of classical
data transmission emerges. Based on the above findings we argue for a new
approach to optical communication network design, wherein in-line amplifiers
are replaced by novel fiber supporting high spectral bandwidth to allow for
noiseless data transmission in the quantum limit.Comment: This version has a significantly shortened abstract, and an expanded
section on transmission at high baud-rate
Performance of Coherent Frequency-Shift Keying for Classical Communication on Quantum Channels
No full textWe evaluate the performance of coherent frequency-shift keying (CFSK) [1], [2] alphabets for communication on quantum channels. We show that, contrarily to what previously thought, the square-root-measurement (SRM) is sub-optimal for discriminating CFSK states. Furthermore, we compute the maximum information transmission rate of the CFSK alphabet, observing that it employs at least as many frequency modes as the signal states, and compare it with standard phase-shift-keying. Finally, we introduce a discretized CFSK alphabet with higher mode-efficiency, exhibiting comparable error-probability performance with respect to CFSK and better rate performance. Our results suggest the existence of a tradeoff between the CFSK reduced error-probability and its mode efficiency
Coherent-state discrimination via nonheralded probabilistic amplification
Full text linkA scheme for the detection of low-intensity optical coherent signals was studied which uses a probabilistic amplifier operated in the nonheralded version as the underlying nonlinear operation to improve the detection efficiency. This approach allows us to improve the statistics by keeping track of all possible outcomes of the amplification stage (including failures). When compared with an optimized Kennedy receiver, the resulting discrimination success probability we obtain presents a gain up to â1⁄41.85% and it approaches the Helstrom bound appreciably faster than the Dolinar receiver when employed in an adaptive strategy. We also notice that the advantages obtained can ultimately be associated with the fact that, in the high-gain limit, the nonheralded version of the probabilistic amplifier induces a partial dephasing which preserves quantum coherence among low-energy eigenvectors while removing it elsewhere. A proposal to realize such a transformation based on an optical cavity implementation is presented
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