Quantum linear amplifier enhanced by photon subtraction and addition

Abstract

A deterministic quantum amplifier inevitably adds noise to an amplified signal due to the uncertainty principle in quantum physics. We here investigate how a quantum-noise-limited amplifier can be improved by additionally employing the photon subtraction, the photon addition, and a coherent superposition of the two, thereby making a probabilistic, heralded, quantum amplifier. We show that these operations can enhance the performance in amplifying a coherent state in terms of intensity gain, fidelity, and phase uncertainty. In particular, the photon subtraction turns out to be optimal for the fidelity and the phase concentration among these elementary operations, while the photon addition also provides a significant reduction in the phase uncertainty with the largest gain effect.

Nondeterministic noiseless amplification via non-symplectic phase space transformations

“…An ingenious recent approach is to circumvent these limits by designing devices that achieve genuinely noiseless amplifications in a nondeterministic but heralded manner [17]. This noiseless linear amplifier (NLA) has been the subject of considerable theoretical [18][19][20][21][22][23][24][25][26][27][28][29][30] and experimental [31][32][33][34][35][36][37][38] work. Applications in QKD with both continuous variable (CV) [20][21][22] and discrete variables [29,30] have been considered as well as error correction [19].…”

“…This operation will result in an arbitrarily good approximation of an ideal NLA as N increases at the price of a decreased, but finite, success probability. In the second kind of analysis works thus far have utilized particular linear optics implementations such as that of the original proposal [17] or those based upon photon addition and subtraction [26][27][28].…”

Nonclassicality generated by repeatedly operating photon annihilation-then-creation and creation-then-annihilation on squeezed vacuum

“…2, we plot the PNDs of the ACSV and the CASV in the same bar graph for different m and n by using Eqs. (13) and (14). It is found that the ACSV and the CASV are only the even photon number distribution (remaining the main characteristic of the SV) but change the probability value of the SV…”

“…It is shown that these operations enable us to generate highly nonclassical quantum states [8], such as photon-addition coherent state, photon-added thermal states [9][10][11], photon-subtracted squeezed states [12,13], and so on. In addition, single photon operations such as photon subtraction and addition can enhance quantum linear amplifier [14], continuousvariable quantum key distribution [15], entanglement [16][17][18][19], nonlocality [21][22][23], multipartite quantum correlation [20], and the fidelity of continuous variable teleportation [24][25][26]. The entanglement distillation can also be achieved by performing photon subtraction or addition combined with coherent displacement or local squeezing [27][28][29].…”

Experimental noiseless linear amplification using weak measurements

“…By contrast the photon addition-then-subtraction scheme, for a single stage implementation [12], operates at a fixed gain but can be used for slightly larger inputs while maintaining high fidelity operation. However for small input states, the photon-addition-then-subtraction scheme performs with lower state fidelity than the quantum scissors approach and with lower probability of success [18]. Although the gain can be increased, it requires use of additional stages which further reduces the probability of success of this scheme [19].…”