qntm cmptr s cmptr tht xplts qntm mchncl phnmn. n smll scls, physcl mttr xhbts prprts f bth prtcls nd wvs, nd qntm cmptng lvrgs ths bhvr sng spclzd hrdwr. Clsscl physcs cnnt xpln th prtn f ths qntm dvcs, nd sclbl qntm cmptr cld prfrm sm clcltns xpnntlly fstr thn ny mdrn "clsscl" cmptr. Thrtclly lrg-scl qntm cmptr cld brk sm wdly sd ncryptn schms nd d physcsts n prfrmng physcl smltns; hwvr, th crrnt stt f th rt s lrgly xprmntl nd mprctcl, wth svrl bstcls t sfl pplctns.
Th bsc nt f nfrmtn n qntm cmptng, th qbt (r "qntm bt"), srvs th sm fnctn s th bt n clsscl cmptng. Hwvr, nlk clsscl bt, whch cn b n n f tw stts ( bnry), qbt cn xst n sprpstn f ts tw "bss" stts, stt tht s n n bstrct sns "btwn" th tw bss stts. Whn msrng qbt, th rslt s prbblstc tpt f clsscl bt. f qntm cmptr mnplts th qbt n prtclr wy, wv ntrfrnc ffcts cn mplfy th dsrd msrmnt rslts. Th dsgn f qntm lgrthms nvlvs crtng prcdrs tht llw qntm cmptr t prfrm clcltns ffcntly nd qckly.
Qntm cmptrs r nt yt prctcl fr rl wrk. Physclly ngnrng hgh-qlty qbts hs prvn chllngng. f physcl qbt s nt sffcntly sltd frm ts nvrnmnt, t sffrs frm qntm dchrnc, ntrdcng ns nt clcltns. Ntnl gvrnmnts hv nvstd hvly n xprmntl rsrch tht ms t dvlp sclbl qbts wth lngr chrnc tms nd lwr rrr rts. xmpl mplmnttns ncld sprcndctrs (whch slt n lctrcl crrnt by lmntng lctrcl rsstnc) nd n trps (whch cnfn sngl tmc prtcl sng lctrmgntc flds).
n prncpl, clsscl cmptr cn slv th sm cmpttnl prblms s qntm cmptr, gvn ngh tm. Qntm dvntg cms n th frm f tm cmplxty rthr thn cmptblty, nd qntm cmplxty thry shws tht sm qntm lgrthms r xpnntlly mr ffcnt thn th bst-knwn clsscl lgrthms. lrg-scl qntm cmptr cld n thry slv cmpttnl prblms nslvbl by clsscl cmptr n ny rsnbl mnt f tm. Ths cncpt f xtr blty hs bn clld "qntm sprmcy". Whl sch clms hv drwn sgnfcnt ttntn t th dscpln, nr-trm prctcl s css rmn lmtd.