



01935nas a2200145   4500008004100000245005100041210005100092260001300143520152400156100001801680700001901698700001701717700001801734856003701752       2021                        eng d00aQuantum Meets the Minimum Circuit Size Problem0 aQuantum Meets the Minimum Circuit Size Problem  c8/6/20213 a<p>In this work, we initiate the study of the Minimum Circuit Size Problem (MCSP) in the quantum setting. MCSP is a problem to compute the circuit complexity of Boolean functions. It is a fascinating problem in complexity theory---its hardness is mysterious, and a better understanding of its hardness can have surprising implications to many fields in computer science.<br />We first define and investigate the basic complexity-theoretic properties of minimum quantum circuit size problems for three natural objects: Boolean functions, unitaries, and quantum states. We show that these problems are not trivially in NP but in QCMA (or have QCMA protocols). Next, we explore the relations between the three quantum MCSPs and their variants. We discover that some reductions that are not known for classical MCSP exist for quantum MCSPs for unitaries and states, e.g., search-to-decision reduction and self-reduction. Finally, we systematically generalize results known for classical MCSP to the quantum setting (including quantum cryptography, quantum learning theory, quantum circuit lower bounds, and quantum fine-grained complexity) and also find new connections to tomography and quantum gravity. Due to the fundamental differences between classical and quantum circuits, most of our results require extra care and reveal properties and phenomena unique to the quantum setting. Our findings could be of interest for future studies, and we post several open problems for further exploration along this direction.</p>1 aChia, Nai-Hui1 aChou, Chi-Ning1 aZhang, Jiayu1 aZhang, Ruizhe  uhttps://arxiv.org/abs/2108.03171